As far as posting from Tapatalk, use the "..." button on the upper right (selecting "reply" from the options). do NOT use the "Write a Reply" box on the bottom. That won't pull up the necessary icons on the phone app, at least not on my Apple 4s.
Select the square icon of the sun & mountain (between the camera and Twitter icon). It will go to your phone's library where you can select the photo(s) you want to post.