I would like to put several pictures in a row (10-20) over an existing picture / video.
This should probably be in the Feature Requests forum, not here.
Not sure what you're asking for, anyway -- do you mean you want to "stack" 10 to 20 images on top of each other? Place 10 to 20 images on the same slide at the same time so that they all show (they'd end up pretty small to do that)? You need to be more specific in what you're trying to accomplish.
The maximum number of layers currently allowed in FotoMagico is 6 (that includes both image layers AND title layers). It would be nice to have more (a number of us have previously suggested that) -- but right now that's all you can have.