The easiest way is to hit 'enter' right after you've pasted in a photo, to move the cursor down a line. Then you can continue typing, or hit the 'Insert/edit picture' icon to add another photo.
If you 'lose' the cursor...as sometimes happens to me, since the reply box is so narrow...hit the 'End' key on your keyboard, and it should drop the cursor to the bottom of your text box. 