Thanks! Open Graph tags are a great idea. I'm going to add them and push an update soon :) Like you said, this is an improvement over just dropping snapshots into slack, since you keep a lot more information with it (the original link and any conversation on that screenshot).

Initial use case: I think it's really useful if you're developing a website and want to screenshot bugs or feature requests, draw what it should do instead, and add comments (and dismiss when fixed!). I used MarqLink extensively for this while developing MarqLink.