I tried Camera from the gsimageapps:
http://home.gna.org/gsimageapps/
and I found that the app icon is a png. When the application starts, then
in the app icon, and in the Info panel, I only see a white square, instead
of the camera icon. I used gimp to resave the Camera.png as Camera.tif
and tweaked the GNUMakefile to use the tif instead. With the tif I see the
expected Camera icon.
Now I'm wondering what the actual problem is, something in my setup,
something more general problem in -gui? Since this Camera is a relatively
old app, I guess it must have worked at some point in time with the png
image too?