diff --git a/tests/data/REUSE.toml b/tests/data/REUSE.toml
index 79a71e8608502..a2111a539e8d3 100644
--- a/tests/data/REUSE.toml
+++ b/tests/data/REUSE.toml
@@ -100,7 +100,7 @@ SPDX-FileCopyrightText = "2018 Nextcloud GmbH and Nextcloud contributors"
 SPDX-License-Identifier = "AGPL-3.0-or-later"
 
 [[annotations]]
-path = ["integritycheck/mimetypeListModified/core/js/mimetypelist.js", "integritycheck/mimetypeListModified/core/signature.json", "guest_avatar_einstein_32.png", "guest_avatar_einstein_32.svg", "test.pdf"]
+path = ["integritycheck/mimetypeListModified/core/js/mimetypelist.js", "integritycheck/mimetypeListModified/core/signature.json", "test.pdf"]
 precedence = "aggregate"
 SPDX-FileCopyrightText = "2019 Nextcloud GmbH and Nextcloud contributors"
 SPDX-License-Identifier = "AGPL-3.0-or-later"
diff --git a/tests/data/guest_avatar_einstein_32.png b/tests/data/guest_avatar_einstein_32.png
deleted file mode 100644
index d03f0509bac3b..0000000000000
Binary files a/tests/data/guest_avatar_einstein_32.png and /dev/null differ
diff --git a/tests/data/guest_avatar_einstein_32.svg b/tests/data/guest_avatar_einstein_32.svg
deleted file mode 100644
index d007f962f243f..0000000000000
--- a/tests/data/guest_avatar_einstein_32.svg
+++ /dev/null
@@ -1,5 +0,0 @@
-<?xml version="1.0" encoding="UTF-8" standalone="no"?>
-		<svg width="32" height="32" version="1.1" viewBox="0 0 500 500" xmlns="http://www.w3.org/2000/svg">
-			<rect width="100%" height="100%" fill="#499aa2"></rect>
-			<text x="50%" y="350" style="font-weight:normal;font-size:279px;font-family:'Nunito';text-anchor:middle;fill:#fff">E</text>
-		</svg>
diff --git a/tests/lib/Avatar/GuestAvatarTest.php b/tests/lib/Avatar/GuestAvatarTest.php
index eed41e8221e82..cf91454eaaf4e 100644
--- a/tests/lib/Avatar/GuestAvatarTest.php
+++ b/tests/lib/Avatar/GuestAvatarTest.php
@@ -12,6 +12,7 @@
 use OC\Avatar\GuestAvatar;
 use OCP\Files\SimpleFS\InMemoryFile;
 use OCP\IConfig;
+use PHPUnit\Framework\Attributes\DataProvider;
 use Psr\Log\LoggerInterface;
 use Test\TestCase;
 
@@ -37,19 +38,43 @@ public function setupGuestAvatar(): void {
 		$this->guestAvatar = new GuestAvatar('einstein', $config, $logger);
 	}
 
+	public static function themeProvider(): array {
+		return [
+			'light theme' => ['darkTheme' => false, 'backgroundColor' => 0xe9f3f7],
+			'dark theme' => ['darkTheme' => true, 'backgroundColor' => 0x030e12],
+		];
+	}
+
 	/**
-	 * Asserts that testGet() returns the expected avatar.
+	 * Asserts that GuestAvatar::getFile() returns the expected avatar.
 	 *
-	 * For the test a static name "einstein" is used and
-	 * the generated image is compared with an expected one.
+	 * For the test a static name "einstein" is used.
 	 */
-	public function testGet(): void {
-		$avatar = $this->guestAvatar->getFile(32);
+	#[DataProvider('themeProvider')]
+	public function testGet(bool $darkTheme, int $backgroundColor): void {
+		$size = 32;
+		$avatar = $this->guestAvatar->getFile($size, $darkTheme);
 		self::assertInstanceOf(InMemoryFile::class, $avatar);
-		$expectedFile = file_get_contents(
-			__DIR__ . '/../../data/guest_avatar_einstein_32.png'
-		);
-		self::assertEquals(trim($expectedFile), trim($avatar->getContent()));
+		$content = $avatar->getContent();
+		self::assertStringStartsWith("\x89PNG\r\n\x1a\n", $content, 'The avatar is not a PNG');
+
+		$image = imagecreatefromstring($content);
+		self::assertInstanceOf(\GdImage::class, $image);
+		self::assertSame($size, imagesx($image));
+		self::assertSame($size, imagesy($image));
+		self::assertSame($backgroundColor, imagecolorat($image, 0, 0), 'The background is not the guest color');
+
+		// The anti-aliased edges depend on the GD and FreeType versions, the strokes of the letter don't
+		$letterPixels = 0;
+		for ($y = 0; $y < $size; $y++) {
+			for ($x = 0; $x < $size; $x++) {
+				if (imagecolorat($image, $x, $y) === 0x248eb5) {
+					$letterPixels++;
+				}
+			}
+		}
+		// A Noto Sans "E" at 32 px has 27 fully covered pixels
+		self::assertSame(27, $letterPixels, 'The avatar does not show a Noto Sans "E" in the guest color');
 	}
 
 	/**