I tried to use one of those crossword puzzle images to boost but it got declined by Facebook because the text was over the 20% rule.
The Facebook grid tip is a good one, Canva is also a good (pretty inexpensive - images are free or $1 an image I believe) tool to grab an image you can edit / layer text on top of for things like social media posts / blog headers (they have "Facebook" specific sizing and its built to be editable by non-designers):
And there's a good list of similar tools here:
Great question, I would think that Facebook has algorithms and people on tasks to review this simultaneously. Your question regards more so "hacking" into their platform to just promote a picture. Don't know why you are trying to do this, but maybe find another way to promote the pic, such as tweeting it and then promoting that text on facebook or something.