--- a/Image.st	Wed Jan 25 14:22:38 2017 +0100
+++ b/Image.st	Wed Jan 25 16:09:33 2017 +0100
@@ -2180,6 +2180,10 @@
     "Modified: 24.4.1997 / 19:04:52 / cg"
 !
 
+isAbstract
+    ^ self == Image
+!
+
 isImageFileSuffix:aSuffix
     "return true, if the given suffix is known to be an image files suffix"