This has been asked in the past and I feel that it probably won't be possible for the same reason SE doesn't allow personal artwork to be used for FC crests, and that is because of human nature - inevitably someone would think it funny to try and upload something pornographic or offensive as a crest template, and thus SE would have to approve every piece of artwork submitted to ensure it complies with the Terms of Service, a costly and time consuming effort, resources which can be better spent elsewhere.
In the same way, because there would be nothing stopping someone slipping a non-screenshot into the screenshots folder to be used with such a function which could violate the ToS, it's probably more trouble for SE than it's worth to implement sadly. As much as I would
love your idea, realistically I don't think it would be possible sadly.
