Hello
I did try a lot now, but it simply doesn't work:
I created a new background image for the medium size 75x75
After I changed the settings in Options->Main->Images And Detail Window Size Settings to 70x70
After I uploaded the pics
It looks nice in FF but very ugly in IE.
The pics will remain in the lower right corner in IE. In FF they are centered as expected. It only works as long as the medium size of the background image and the pics remains 100x100. But this is to big for my site (and the small size in the galery view ist to small).
It is curious that it works in the galleries overview but not in a single gallery. I don't know what to do else.