Posting photos on forums is one of those things that should be universal like the pedals in a car. Unfortunately, it's not. It is like the credit card readers in stores, all different.
In a thread, I tried posting 6 pictures. When I uploaded the first one, fine. There was no "load more" button so I went ahead and loaded the next, the next, etc. When I previewed, only the last one was there! Seems each upload over writes the last.
I know it can be done as I have seen posts with multiple photos in the body of the text.
How about using the Freerails gallery for your photos? That's what I use and I can post as many pix as the law allows! The gallery is the easiest way I know of to use and post photos, I have tried them all(all that matters!). It's as easy as falling off a log, I have done that also.