Snapchat used to have that feature with the Stickers function but I deleted it once an account was required to use it. iPhone photos has a function that detects people, you can get a PNG of a person out of a photo and crop it. Apart from that I’m not sure what’s out there that can be done while on the pot- I too would like to know what folks have to recommend. You could try cropping out a face and using a background removal tool/app, and then using a photo layer app for the rest, is how I would approach it.