Image error for every image manipulation

Hi,

i`m getting the error fallback image when I e.g. apply resize on an image. Same happens in admin: All images shown for a page only show the error fallback image: /images/f/a/l/l/b/fallback.jpg. Something seems to be wrong with the image manipulation library.

How can I get an error message from Gregwar Image library? It is hard to find was is wrong without having an error message.
Or what else could be wrong? Grav said at installation, that all dependencies exist.

Any ideas on that?

Best regards,

Johannes

Ok, found it by myself:
PHP extension GD was used without JPEG support compiled in.

I had to set $useFallbackImage = true in Gregwar Library sourcecode to see the correct error. I think, that variable should be settable by Grav config.