diff --git a/lib/src/test/org/kiwix/test/libkiwix/TestBook.java b/lib/src/test/org/kiwix/test/libkiwix/TestBook.java
index 7d15d9a..32deb0c 100644
--- a/lib/src/test/org/kiwix/test/libkiwix/TestBook.java
+++ b/lib/src/test/org/kiwix/test/libkiwix/TestBook.java
@@ -2,8 +2,9 @@
 package org.kiwix.test.libkiwix;
 
 import org.kiwix.libkiwix.Book;
-import org.kiwix.libkiwix.Illustration;
+import org.kiwix.test.libkiwix.TestIllustration;
 import org.kiwix.test.libzim.TestArchive;
+import java.util.stream.Stream;
 
 public class TestBook
 {
@@ -35,6 +36,6 @@ public class TestBook
   public long getMediaCount() { return inner.getMediaCount(); }
   public long getSize() { return inner.getSize(); }
 
-  public Illustration[] getIllustrations() { return inner.getIllustrations(); }
-  public Illustration getIllustration(int size) { return inner.getIllustration(size); }
+  public TestIllustration[] getIllustrations() { return Stream.of(inner.getIllustrations()).map(i -> new TestIllustration(i)).toArray(TestIllustration[]::new); }
+  public TestIllustration getIllustration(int size) { return new TestIllustration(inner.getIllustration(size)); }
 }
diff --git a/lib/src/test/org/kiwix/test/libkiwix/TestIllustration.java b/lib/src/test/org/kiwix/test/libkiwix/TestIllustration.java
new file mode 100644
index 0000000..155b9e5
--- /dev/null
+++ b/lib/src/test/org/kiwix/test/libkiwix/TestIllustration.java
@@ -0,0 +1,16 @@
+
+package org.kiwix.test.libkiwix;
+
+import org.kiwix.libkiwix.Illustration;
+
+public class TestIllustration
+{
+  private Illustration inner;
+  public TestIllustration(Illustration _inner) { inner = _inner; }
+
+  public int width() { return inner.width(); }
+  public int height() { return inner.height(); }
+  public String mimeType() { return inner.mimeType(); }
+  public String url() { return inner.url(); }
+  public byte[] getData() { return inner.getData(); }
+}
diff --git a/lib/src/test/test.java b/lib/src/test/test.java
index ba419b0..1044946 100644
--- a/lib/src/test/test.java
+++ b/lib/src/test/test.java
@@ -303,7 +303,7 @@ private void testLibrary(TestLibrary lib)
         TestBook book = lib.getBookById(bookIds[0]);
         assertEquals(book.getTitle(), "Test ZIM file");
         assertEquals(book.getTags(), "_category:Category;_ftindex:yes;_ftindex:yes;_pictures:yes;_videos:yes;_details:yes");
-        assertEquals(book.getIllustration(48).width(), 48);
+
         assertEquals(book.getUrl(), "http://localhost/small.zim");
         assertEquals(book.getDescription(), "Description");
         assertEquals(book.getCreator(), "Creator");
@@ -313,7 +313,7 @@ private void testLibrary(TestLibrary lib)
         assertEquals(book.getArticleCount(), 1);
         assertEquals(book.getMediaCount(), 1);
         assertEquals(book.getSize(), 66560);
-        Illustration[] illustrations = book.getIllustrations();
+        TestIllustration[] illustrations = book.getIllustrations();
         assertEquals(1, illustrations.length);
 
         assertEquals(book.getTagStr("video"), "");
@@ -328,7 +328,15 @@ public void testLibrarySimple() throws IOException {
             testLibrary(lib);
             String[] bookIds = lib.getBooksIds();
             TestBook book = lib.getBookById(bookIds[0]);
-            assertEquals(book.getIllustration(48).url(), "");
+
+            TestIllustration illustration = book.getIllustration(48);
+            assertEquals(illustration.width(), 48);
+            assertEquals(illustration.height(), 48);
+            assertEquals(illustration.mimeType(), "image/png");
+            assertEquals(illustration.url(), "");
+            byte[] faviconData = getFileContent("small_zimfile_data/favicon.png");
+            assertTrue(Arrays.equals(faviconData, illustration.getData()));
+
             assertEquals(book.getPath(), new File("small.zim").getAbsolutePath());
             assertEquals(book.getHumanReadableIdFromPath(), "small");
             assertTrue(book.isPathValid());
@@ -351,7 +359,15 @@ public void testLibraryXml() throws IOException {
             testLibrary(lib);
             String[] bookIds = lib.getBooksIds();
             TestBook book = lib.getBookById(bookIds[0]);
-            assertEquals(book.getIllustration(48).url(), "");
+
+            TestIllustration illustration = book.getIllustration(48);
+            assertEquals(illustration.width(), 48);
+            assertEquals(illustration.height(), 48);
+            assertEquals(illustration.mimeType(), "image/png");
+            assertEquals(illustration.url(), "");
+            byte[] faviconData = getFileContent("small_zimfile_data/favicon.png");
+            assertTrue(Arrays.equals(faviconData, illustration.getData()));
+
             assertEquals(book.getPath(), new File("small.zim").getAbsolutePath());
             assertEquals(book.getHumanReadableIdFromPath(), "small");
             assertTrue(book.isPathValid());
@@ -370,7 +386,15 @@ public void testLibraryXmlContent() throws IOException {
             testLibrary(lib);
             String[] bookIds = lib.getBooksIds();
             TestBook book = lib.getBookById(bookIds[0]);
-            assertEquals(book.getIllustration(48).url(), "");
+
+            TestIllustration illustration = book.getIllustration(48);
+            assertEquals(illustration.width(), 48);
+            assertEquals(illustration.height(), 48);
+            assertEquals(illustration.mimeType(), "image/png");
+            assertEquals(illustration.url(), "");
+            byte[] faviconData = getFileContent("small_zimfile_data/favicon.png");
+            assertTrue(Arrays.equals(faviconData, illustration.getData()));
+
             assertEquals(book.getPath(), new File("small.zim").getAbsolutePath());
             assertEquals(book.getHumanReadableIdFromPath(), "small");
             assertTrue(book.isPathValid());
@@ -389,7 +413,15 @@ public void testLibraryOPDS() throws IOException {
             testLibrary(lib);
             String[] bookIds = lib.getBooksIds();
             TestBook book = lib.getBookById(bookIds[0]);
-            assertEquals(book.getIllustration(48).url(), "http://localhost/meta?name=favicon&content=small");
+
+            TestIllustration illustration = book.getIllustration(48);
+            assertEquals(illustration.width(), 48);
+            assertEquals(illustration.height(), 48);
+            assertEquals(illustration.mimeType(), "image/png");
+            assertEquals(illustration.url(), "http://localhost/meta?name=favicon&content=small");
+            // This will try to downoald to the data, but we have no local server. So return empty array.
+            assertEquals(illustration.getData(), new byte[0]);
+
             assertEquals(book.getPath(), "");
             assertEquals(book.getHumanReadableIdFromPath(), "");
             assertFalse(book.isPathValid());