Heya! The idea behind our rule "Only use assets that you have either created yourself (or team) within the jam period" isn't to force devs to create an entirely new game engine/architecture or framework that is already built-in or should be. The main purpose is to prohibit and discourage entrants from using pre-built projects and assets. For the stock images, I would still provide credit unless you're sure, beyond a reasonable doubt, you wouldn't need to.
Also, the analogue in "analogue-horror" is more or less optional for your entry. The main focus is primarily horror and the entities or anomalies you can think up. It could be something as mundane as a glass of water that never changes and only stays lukewarm, or as silly as a sasquatch that hunts people from a dumpster behind a grocery store. Just try to make it a horror game, even if you don't really know how or if your game counts as horror. We ask entrants to keep in mind this is a horror jam for horror games, but your game doesn't need to fit in perfectly. We certainly encourage you guys to try out something new and experiment with new concepts and ideas. Hope that answers your question and helps to clear up the confusion. Please let me know if you have any more questions, and apologize for the delay!