Did you get an "error" message when trying to post it and if so, what did it say?
If the photos are on your PC you might have to "resize" and/or "reformat" them.
And the easy to do that is, via your photo program, is to "click" on "Save a Copy of" and then select ...... "For E-mail or Web" with "Standard" view, ..... select the ".jpg" format ..... and then upload that copy.