You would just make an original post and make 3 successive replies to get your 20 pics.
i've had to do that a few times with some of my project threads, not really a big deal. Just to make sure I get the several posts all in a row, I reply to myself the several times right away so it is like a place-holder for posting the additional pictures.
..Just to make sure I get the several posts all in a row, I reply to myself the several times right away so it is like a place-holder for posting the additional pictures.