You could do this with a standard marker (like the corner parts of a QR code) on a piece of transparent adhesive plastic, paired with a database. Turn anything into a QR code.
In theory you could do it without the plastic sticker on the lookup side, but it seems like you'd use far more resources with little gain (principle gain being you only need one transparent marker; principle loss, you have to search every image for every "marker code" ever created across every part of the image).
In theory you could do it without the plastic sticker on the lookup side, but it seems like you'd use far more resources with little gain (principle gain being you only need one transparent marker; principle loss, you have to search every image for every "marker code" ever created across every part of the image).