We will probably not code this for you. You can make the change yourself, probably without not too much trouble. But first you will need to familiarize yourself with the Zenphoto theming tutorial on the WEB site.
THX, but could you tell me in which php file I can find the decalration of the tumb.obj. I have been looking inside the image-class php file but didn´t find the exact line, maybe you could help me here