You are not alone, Astra....
I have no problem with writing comments on pics I post to the main OG site. My problem occurs when posting pics on a discussion thread like this.
Can you tell me the picture in question so I can look into it?
Lalalava is right, as the 2 pics are from the same user, and his profile is set to "private"
Ok, I see that. My guess is that he's got his profile set to only friends being able to leave comments on his pics. I don't know why someone would have that setting though.