Hmm the GD library seems to be OK (see attachment). The weirdest issue is that I can upload a png file, but when I try to open it, it gives a 500 internal server error.
Is there maybe any module to read files/images in another way?
i just had the same problem on a box where a system update didn't update the libraries correctly, so everytime the gd function imagecreatefrompng($png) was called, apache aborted (similar to this thread)
Recompiling the libraries solved the problem for me.