<cut and past from separate email to Dana on this issue>
We made a number of decisions while developing AutoCollage to try to ensure the program is stable and performs as well as possible. One of those decisions was to restrict images which can be collaged to locally available files. When the network is quick and working well, network images aren't a problem. However, a huge number of things can go wrong with accessing images over a network, which makes supporting network images consistently a significant work item.
Thank you for your feedback. We're making note of feature requests, and will ensure the ability to read images from the network is on the list.