Hello,

I am sorry I forgot to post the solution to this problem.

In the end all I needed to do was copying the dir "imageformats" in the dir containing the executable.
Of course the one provided with Qt contains more than I need, so I just removed all the unnecessary files.
This way it displays correctly the background image also on other computers.

I found a useful description in:http://doc.trolltech.com/qq/qq10-win...eployment.html under plugins.

Thank you very much Lykurg for all your help!