I’ll answer my own question. The function “imagecreatefromjpeg()” are a part of the gd-module to apache. This module does not come with jpeg support out of the box, you need to add a argument when you compile apacke. So if you get this error you need to activate jpeg supoprt in gd, and if you don’t controll the apacke installation, talk you or hostmaster.
A quick fix is to use png images and not jpeg, but this has some disavantages.