[TYPO3-dev] Cannot get image processing to work

[Uschi Renziehausen]

Hi folks,

I am in the middle of launching a project, fe works fine so far, but for one or the other reason the install tools says 
that I have no im installed, so no image processing at all. I am sure the given paths are correct and if I try to 
execute the same commands as the install tool via the command line I get a proper result. But once I try it with exec(), 
  I do not get anything at all. So I suppose this must have to do with our php configuration/installation. Any hints 
what might be the reason?

Thanks in advance for your help,

Uschi (a little bit desperate)