Image is empty?

[David Bovill]

How do I test to see if an image is empty?

The issue is that it is hard to filter the file dialog in such a way  
that only images or videos are selectable cross platform and then you  
have drag and drop... so I tried testing after a drag and drop (which  
sets the filename property) to see if the image has any data... so if  
you choose a text file or pdf the filename property is set (which is  
a pitty) and the imageData is not empy...

There is nothing that I now of like "file is an image"...

Any ideas of how to figure out after setting the filename of an image  
whether it worked or not?