Rings a bell: https://jalbum.net/forum/thread.jspa?threadID=53902
ETA: This could get really messy. Which image filters to apply? Straightening, surely, and color corrections too. But cropping, watermarking, logo overlay, and so on? Probably not.
I think I would just say "Start a project with only your theme image, choose huge image bounds, do your image editing, grab the output slide image, and use that in your real project."