How do I add movie stills to the Conformist's detail page?

(N.B., Sorry, but I didn't check all five pages of threads on this movie before asking this question.

So, I wanted to use some photos from this movie to talk about the stylish use of the blinds to cast bars of light on the characters. However, there are only twelve pictures on the Conformist's detail page as of today (Aug 24, 2016).

I downloaded two from the web and tried to upload one by clicking on "Add photo" -- but all I got was a blank grey square. Is there some secret formula?

FWIW, I am a new member, and I am not using imdbpro. Do I have to pay real money to do this? 'Cause I'm just not ready to make that big jump... :D