If you are on the page for an individual image (having clicked on the thumbnail displayed on a profile) there are two possible reasons you can't see the add comment box: 1) you are not logged in 2) the owner of the profile has chosen not to recieve comments.
I see what you're saying stolenfaces, but I mean I can't see the comments made on MY images. I recently subscribed and expanded my profile on here and I've had a couple of comments. I just wanted to see what they were. On my mobile I can see the comment but not the image, on my lappy I can see a comment has been made but can't actually read it.
do not click on My Images.....click on your own name as is you were checking out someone else s profile. ie...at the top of the page is 'You are logged in as Jackass' click your name you will visit your own profile as a 'guest' you will be able to click an image and add comments from there.