"Our photos are on the computer."
Is this only correct with the 里? Would other prepositions or none at all be acceptable?
"In" or "inside". The differences in English are subtle. Also, translating prepositions between languages is never straightforward and always quite idiomatic.
"In" actually makes more sense than "on" when you think about it, but idiomatically in English we use "on". Chinese seems to use the more sensible "li" (in).