diff --git a/lib/private/Avatar/UserAvatar.php b/lib/private/Avatar/UserAvatar.php
index f47809425ed40..8573adf5d87c0 100644
--- a/lib/private/Avatar/UserAvatar.php
+++ b/lib/private/Avatar/UserAvatar.php
@@ -122,7 +122,7 @@ public function set($data) {
 	/**
 	 * Returns an image from several sources.
 	 *
-	 * @param IImage|resource|string $data An image object, imagedata or path to the avatar
+	 * @param IImage|resource|string|\GdImage $data An image object, imagedata or path to the avatar
 	 * @return IImage
 	 */
 	private function getAvatarImage($data) {
@@ -131,7 +131,10 @@ private function getAvatarImage($data) {
 		}
 
 		$img = new OC_Image();
-		if (is_resource($data) && get_resource_type($data) === 'gd') {
+		if (
+			(is_resource($data) && get_resource_type($data) === 'gd') ||
+			(is_object($data) && get_class($data) === \GdImage::class)
+			) {
 			$img->setResource($data);
 		} elseif (is_resource($data)) {
 			$img->loadFromFileHandle($data);
diff --git a/lib/private/Preview/Bitmap.php b/lib/private/Preview/Bitmap.php
index 7322e07ab3454..b573808447646 100644
--- a/lib/private/Preview/Bitmap.php
+++ b/lib/private/Preview/Bitmap.php
@@ -61,7 +61,7 @@ public function getThumbnail(File $file, int $maxX, int $maxY): ?IImage {
 
 		//new bitmap image object
 		$image = new \OC_Image();
-		$image->loadFromData($bp);
+		$image->loadFromData((string) $bp);
 		//check if image object is valid
 		return $image->valid() ? $image : null;
 	}
diff --git a/lib/private/Preview/HEIC.php b/lib/private/Preview/HEIC.php
index f9f85090a8008..43d1cf65ada6e 100644
--- a/lib/private/Preview/HEIC.php
+++ b/lib/private/Preview/HEIC.php
@@ -77,7 +77,7 @@ public function getThumbnail(File $file, int $maxX, int $maxY): ?IImage {
 
 		//new bitmap image object
 		$image = new \OC_Image();
-		$image->loadFromData($bp);
+		$image->loadFromData((string) $bp);
 		//check if image object is valid
 		return $image->valid() ? $image : null;
 	}
diff --git a/lib/private/Preview/SVG.php b/lib/private/Preview/SVG.php
index 6630dc2697876..790dad5c26cd2 100644
--- a/lib/private/Preview/SVG.php
+++ b/lib/private/Preview/SVG.php
@@ -70,7 +70,7 @@ public function getThumbnail(File $file, int $maxX, int $maxY): ?IImage {
 
 		//new image object
 		$image = new \OC_Image();
-		$image->loadFromData($svg);
+		$image->loadFromData((string) $svg);
 		//check if image object is valid
 		if ($image->valid()) {
 			$image->scaleDownToFit($maxX, $maxY);
diff --git a/lib/private/legacy/OC_Image.php b/lib/private/legacy/OC_Image.php
index ed173849c769c..f93bcfaaaf481 100644
--- a/lib/private/legacy/OC_Image.php
+++ b/lib/private/legacy/OC_Image.php
@@ -102,7 +102,7 @@ public function valid() { // apparently you can't name a method 'empty'...
 		if (is_resource($this->resource)) {
 			return true;
 		}
-		if (is_object($this->resource) && get_class($this->resource) === 'GdImage') {
+		if (is_object($this->resource) && get_class($this->resource) === \GdImage::class) {
 			return true;
 		}
 
@@ -309,7 +309,7 @@ public function __invoke() {
 	}
 
 	/**
-	 * @param resource Returns the image resource in any.
+	 * @param resource|\GdImage $resource
 	 * @throws \InvalidArgumentException in case the supplied resource does not have the type "gd"
 	 */
 	public function setResource($resource) {
@@ -319,7 +319,7 @@ public function setResource($resource) {
 			return;
 		}
 		// PHP 8 has real objects for GD stuff
-		if (is_object($resource) && get_class($resource) === 'GdImage') {
+		if (is_object($resource) && get_class($resource) === \GdImage::class) {
 			$this->resource = $resource;
 			return;
 		}
@@ -327,7 +327,7 @@ public function setResource($resource) {
 	}
 
 	/**
-	 * @return resource Returns the image resource in any.
+	 * @return resource|\GdImage Returns the image resource in any.
 	 */
 	public function resource() {
 		return $this->resource;
@@ -537,7 +537,7 @@ public function fixOrientation() {
 	 * It is the responsibility of the caller to position the pointer at the correct place and to close the handle again.
 	 *
 	 * @param resource $handle
-	 * @return resource|false An image resource or false on error
+	 * @return resource|\GdImage|false An image resource or false on error
 	 */
 	public function loadFromFileHandle($handle) {
 		$contents = stream_get_contents($handle);
@@ -551,7 +551,7 @@ public function loadFromFileHandle($handle) {
 	 * Loads an image from a local file.
 	 *
 	 * @param bool|string $imagePath The path to a local file.
-	 * @return bool|resource An image resource or false on error
+	 * @return bool|resource|\GdImage An image resource or false on error
 	 */
 	public function loadFromFile($imagePath = false) {
 		// exif_imagetype throws "read error!" if file is less than 12 byte
@@ -667,17 +667,17 @@ public function loadFromFile($imagePath = false) {
 	 * Loads an image from a string of data.
 	 *
 	 * @param string $str A string of image data as read from a file.
-	 * @return bool|resource An image resource or false on error
+	 * @return bool|resource|\GdImage An image resource or false on error
 	 */
 	public function loadFromData($str) {
-		if (is_resource($str)) {
+		if (!is_string($str)) {
 			return false;
 		}
 		$this->resource = @imagecreatefromstring($str);
 		if ($this->fileInfo) {
 			$this->mimeType = $this->fileInfo->buffer($str);
 		}
-		if (is_resource($this->resource)) {
+		if ($this->valid()) {
 			imagealphablending($this->resource, false);
 			imagesavealpha($this->resource, true);
 		}
@@ -693,7 +693,7 @@ public function loadFromData($str) {
 	 * Loads an image from a base64 encoded string.
 	 *
 	 * @param string $str A string base64 encoded string of image data.
-	 * @return bool|resource An image resource or false on error
+	 * @return bool|resource|\GdImage An image resource or false on error
 	 */
 	public function loadFromBase64($str) {
 		if (!is_string($str)) {
@@ -723,7 +723,7 @@ public function loadFromBase64($str) {
 	 * @param string $fileName <p>
 	 * Path to the BMP image.
 	 * </p>
-	 * @return bool|resource an image resource identifier on success, <b>FALSE</b> on errors.
+	 * @return bool|resource|\GdImage an image resource identifier on success, <b>FALSE</b> on errors.
 	 */
 	private function imagecreatefrombmp($fileName) {
 		if (!($fh = fopen($fileName, 'rb'))) {
@@ -879,12 +879,12 @@ public function resize($maxSize) {
 		$result = $this->resizeNew($maxSize);
 		imagedestroy($this->resource);
 		$this->resource = $result;
-		return is_resource($result);
+		return $this->valid();
 	}
 
 	/**
 	 * @param $maxSize
-	 * @return resource | bool
+	 * @return resource|bool|\GdImage
 	 */
 	private function resizeNew($maxSize) {
 		if (!$this->valid()) {
@@ -915,14 +915,14 @@ public function preciseResize(int $width, int $height): bool {
 		$result = $this->preciseResizeNew($width, $height);
 		imagedestroy($this->resource);
 		$this->resource = $result;
-		return is_resource($result);
+		return $this->valid();
 	}
 
 
 	/**
 	 * @param int $width
 	 * @param int $height
-	 * @return resource | bool
+	 * @return resource|bool|\GdImage
 	 */
 	public function preciseResizeNew(int $width, int $height) {
 		if (!$this->valid()) {
@@ -1024,7 +1024,7 @@ public function crop(int $x, int $y, int $w, int $h): bool {
 		$result = $this->cropNew($x, $y, $w, $h);
 		imagedestroy($this->resource);
 		$this->resource = $result;
-		return is_resource($result);
+		return $this->valid();
 	}
 
 	/**
@@ -1192,7 +1192,7 @@ public function __destruct() {
 	 * @link http://www.programmierer-forum.de/imagebmp-gute-funktion-gefunden-t143716.htm
 	 * @author mgutt <marc@gutt.it>
 	 * @version 1.00
-	 * @param resource $im
+	 * @param resource|\GdImage $im
 	 * @param string $fileName [optional] <p>The path to save the file to.</p>
 	 * @param int $bit [optional] <p>Bit depth, (default is 24).</p>
 	 * @param int $compression [optional]
diff --git a/lib/public/IImage.php b/lib/public/IImage.php
index aa1cf344e5fc2..ea9f6e40190c0 100644
--- a/lib/public/IImage.php
+++ b/lib/public/IImage.php
@@ -99,7 +99,7 @@ public function show($mimeType = null);
 	public function save($filePath = null, $mimeType = null);
 
 	/**
-	 * @return resource Returns the image resource in any.
+	 * @return resource|\GdImage Returns the image resource in any.
 	 * @since 8.1.0
 	 */
 	public function resource();
diff --git a/psalm-ocp.xml b/psalm-ocp.xml
index 5574ae0fb5dc1..4519b7e9ca46a 100644
--- a/psalm-ocp.xml
+++ b/psalm-ocp.xml
@@ -16,4 +16,12 @@
 	<extraFiles>
 		<directory name="3rdparty"/>
 	</extraFiles>
+	<issueHandlers>
+		<UndefinedDocblockClass>
+			<errorLevel type="suppress">
+				<!-- Classes from PHP>=8 -->
+				<referencedClass name="GdImage" />
+			</errorLevel>
+		</UndefinedDocblockClass>
+	</issueHandlers>
 </psalm>
diff --git a/psalm.xml b/psalm.xml
index a075ceb24a786..4f75af61dde9f 100644
--- a/psalm.xml
+++ b/psalm.xml
@@ -81,6 +81,8 @@
 			<errorLevel type="suppress">
 				<referencedClass name="OCA\GroupFolders\Mount\GroupFolderStorage"/>
 				<referencedClass name="OCA\TwoFactorNextcloudNotification\Controller\APIController"/>
+				<!-- Classes from PHP>=8 (needed to be able to use \GdImage::class) -->
+				<referencedClass name="GdImage" />
 			</errorLevel>
 		</UndefinedClass>
 		<UndefinedFunction>
@@ -124,6 +126,8 @@
 				<!-- Helper classes for sharing API integration from other apps -->
 				<referencedClass name="OCA\Deck\Sharing\ShareAPIHelper" />
 				<referencedClass name="OCA\Talk\Share\Helper\DeletedShareAPIController" />
+				<!-- Classes from PHP>=8 -->
+				<referencedClass name="GdImage" />
 			</errorLevel>
 		</UndefinedDocblockClass>
 	</issueHandlers>
diff --git a/tests/lib/Avatar/UserAvatarTest.php b/tests/lib/Avatar/UserAvatarTest.php
index 31f2a6ebf5bd5..6c902e10829c2 100644
--- a/tests/lib/Avatar/UserAvatarTest.php
+++ b/tests/lib/Avatar/UserAvatarTest.php
@@ -52,10 +52,6 @@ public function avatarTextData() {
 	}
 
 	public function testGetNoAvatar() {
-		if (PHP_MAJOR_VERSION > 7) {
-			$this->markTestSkipped('Only run on php7');
-		}
-
 		$file = $this->createMock(ISimpleFile::class);
 		$this->folder->method('newFile')
 			->willReturn($file);
@@ -91,10 +87,6 @@ public function testGetNoAvatar() {
 	}
 
 	public function testGetAvatarSizeMatch() {
-		if (PHP_MAJOR_VERSION > 7) {
-			$this->markTestSkipped('Only run on php7');
-		}
-
 		$this->folder->method('fileExists')
 			->willReturnMap([
 				['avatar.jpg', true],
@@ -112,10 +104,6 @@ public function testGetAvatarSizeMatch() {
 	}
 
 	public function testGetAvatarSizeMinusOne() {
-		if (PHP_MAJOR_VERSION > 7) {
-			$this->markTestSkipped('Only run on php7');
-		}
-
 		$this->folder->method('fileExists')
 			->willReturnMap([
 				['avatar.jpg', true],
@@ -132,10 +120,6 @@ public function testGetAvatarSizeMinusOne() {
 	}
 
 	public function testGetAvatarNoSizeMatch() {
-		if (PHP_MAJOR_VERSION > 7) {
-			$this->markTestSkipped('Only run on php7');
-		}
-
 		$this->folder->method('fileExists')
 			->willReturnMap([
 				['avatar.png', true],
@@ -200,10 +184,6 @@ public function testExistsPNG() {
 	}
 
 	public function testSetAvatar() {
-		if (PHP_MAJOR_VERSION > 7) {
-			$this->markTestSkipped('Only run on php7');
-		}
-
 		$avatarFileJPG = $this->createMock(File::class);
 		$avatarFileJPG->method('getName')
 			->willReturn('avatar.jpg');
diff --git a/tests/lib/ImageTest.php b/tests/lib/ImageTest.php
index ebf00392d875f..5b83c4ac57fbb 100644
--- a/tests/lib/ImageTest.php
+++ b/tests/lib/ImageTest.php
@@ -20,10 +20,6 @@ public static function tearDownAfterClass(): void {
 	}
 
 	public function testConstructDestruct() {
-		if (PHP_MAJOR_VERSION > 7) {
-			$this->markTestSkipped('Only run on php7');
-		}
-
 		$img = new \OC_Image();
 		$img->loadFromFile(OC::$SERVERROOT.'/tests/data/testimage.png');
 		$this->assertInstanceOf('\OC_Image', $img);
@@ -51,10 +47,6 @@ public function testConstructDestruct() {
 	}
 
 	public function testValid() {
-		if (PHP_MAJOR_VERSION > 7) {
-			$this->markTestSkipped('Only run on php7');
-		}
-
 		$img = new \OC_Image();
 		$img->loadFromFile(OC::$SERVERROOT.'/tests/data/testimage.png');
 		$this->assertTrue($img->valid());
@@ -69,10 +61,6 @@ public function testValid() {
 	}
 
 	public function testMimeType() {
-		if (PHP_MAJOR_VERSION > 7) {
-			$this->markTestSkipped('Only run on php7');
-		}
-
 		$img = new \OC_Image();
 		$img->loadFromFile(OC::$SERVERROOT.'/tests/data/testimage.png');
 		$this->assertEquals('image/png', $img->mimeType());
@@ -90,10 +78,6 @@ public function testMimeType() {
 	}
 
 	public function testWidth() {
-		if (PHP_MAJOR_VERSION > 7) {
-			$this->markTestSkipped('Only run on php7');
-		}
-
 		$img = new \OC_Image();
 		$img->loadFromFile(OC::$SERVERROOT.'/tests/data/testimage.png');
 		$this->assertEquals(128, $img->width());
@@ -111,10 +95,6 @@ public function testWidth() {
 	}
 
 	public function testHeight() {
-		if (PHP_MAJOR_VERSION > 7) {
-			$this->markTestSkipped('Only run on php7');
-		}
-
 		$img = new \OC_Image();
 		$img->loadFromFile(OC::$SERVERROOT.'/tests/data/testimage.png');
 		$this->assertEquals(128, $img->height());
@@ -132,10 +112,6 @@ public function testHeight() {
 	}
 
 	public function testSave() {
-		if (PHP_MAJOR_VERSION > 7) {
-			$this->markTestSkipped('Only run on php7');
-		}
-
 		$img = new \OC_Image();
 		$img->loadFromFile(OC::$SERVERROOT.'/tests/data/testimage.png');
 		$img->resize(16);
@@ -150,10 +126,6 @@ public function testSave() {
 	}
 
 	public function testData() {
-		if (PHP_MAJOR_VERSION > 7) {
-			$this->markTestSkipped('Only run on php7');
-		}
-
 		$img = new \OC_Image();
 		$img->loadFromFile(OC::$SERVERROOT.'/tests/data/testimage.png');
 		$raw = imagecreatefromstring(file_get_contents(OC::$SERVERROOT.'/tests/data/testimage.png'));
@@ -188,10 +160,6 @@ public function testData() {
 	}
 
 	public function testDataNoResource() {
-		if (PHP_MAJOR_VERSION > 7) {
-			$this->markTestSkipped('Only run on php7');
-		}
-
 		$img = new \OC_Image();
 		$this->assertNull($img->data());
 	}
@@ -200,10 +168,6 @@ public function testDataNoResource() {
 	 * @depends testData
 	 */
 	public function testToString() {
-		if (PHP_MAJOR_VERSION > 7) {
-			$this->markTestSkipped('Only run on php7');
-		}
-
 		$img = new \OC_Image();
 		$img->loadFromFile(OC::$SERVERROOT.'/tests/data/testimage.png');
 		$expected = base64_encode($img->data());
@@ -221,10 +185,6 @@ public function testToString() {
 	}
 
 	public function testResize() {
-		if (PHP_MAJOR_VERSION > 7) {
-			$this->markTestSkipped('Only run on php7');
-		}
-
 		$img = new \OC_Image();
 		$img->loadFromFile(OC::$SERVERROOT.'/tests/data/testimage.png');
 		$this->assertTrue($img->resize(32));
@@ -245,10 +205,6 @@ public function testResize() {
 	}
 
 	public function testPreciseResize() {
-		if (PHP_MAJOR_VERSION > 7) {
-			$this->markTestSkipped('Only run on php7');
-		}
-
 		$img = new \OC_Image();
 		$img->loadFromFile(OC::$SERVERROOT.'/tests/data/testimage.png');
 		$this->assertTrue($img->preciseResize(128, 512));
@@ -269,10 +225,6 @@ public function testPreciseResize() {
 	}
 
 	public function testCenterCrop() {
-		if (PHP_MAJOR_VERSION > 7) {
-			$this->markTestSkipped('Only run on php7');
-		}
-
 		$img = new \OC_Image();
 		$img->loadFromFile(OC::$SERVERROOT.'/tests/data/testimage.png');
 		$img->centerCrop();
@@ -293,10 +245,6 @@ public function testCenterCrop() {
 	}
 
 	public function testCrop() {
-		if (PHP_MAJOR_VERSION > 7) {
-			$this->markTestSkipped('Only run on php7');
-		}
-
 		$img = new \OC_Image();
 		$img->loadFromFile(OC::$SERVERROOT.'/tests/data/testimage.png');
 		$this->assertTrue($img->crop(0, 0, 50, 20));
@@ -332,10 +280,6 @@ public static function sampleProvider() {
 	 * @param int[] $expected
 	 */
 	public function testFitIn($filename, $asked, $expected) {
-		if (PHP_MAJOR_VERSION > 7) {
-			$this->markTestSkipped('Only run on php7');
-		}
-
 		$img = new \OC_Image();
 		$img->loadFromFile(OC::$SERVERROOT . '/tests/data/' . $filename);
 		$this->assertTrue($img->fitIn($asked[0], $asked[1]));
@@ -359,10 +303,6 @@ public static function sampleFilenamesProvider() {
 	 * @param string $filename
 	 */
 	public function testScaleDownToFitWhenSmallerAlready($filename) {
-		if (PHP_MAJOR_VERSION > 7) {
-			$this->markTestSkipped('Only run on php7');
-		}
-
 		$img = new \OC_Image();
 		$img->loadFromFile(OC::$SERVERROOT.'/tests/data/' . $filename);
 		$currentWidth = $img->width();
@@ -396,10 +336,6 @@ public static function largeSampleProvider() {
 	 * @param int[] $expected
 	 */
 	public function testScaleDownWhenBigger($filename, $asked, $expected) {
-		if (PHP_MAJOR_VERSION > 7) {
-			$this->markTestSkipped('Only run on php7');
-		}
-
 		$img = new \OC_Image();
 		$img->loadFromFile(OC::$SERVERROOT.'/tests/data/' . $filename);
 		//$this->assertTrue($img->scaleDownToFit($asked[0], $asked[1]));
@@ -420,10 +356,6 @@ public function convertDataProvider() {
 	 * @dataProvider convertDataProvider
 	 */
 	public function testConvert($mimeType) {
-		if (PHP_MAJOR_VERSION > 7) {
-			$this->markTestSkipped('Only run on php7');
-		}
-
 		$img = new \OC_Image();
 		$img->loadFromFile(OC::$SERVERROOT.'/tests/data/testimage.png');
 		$tempFile = tempnam(sys_get_temp_dir(), 'img-test');