First of all, i want to say that it's a great site, and it continues to improve constantly. I have one small suggestion to make:
Currently, to get to the parent image from the child one, you have the "parent" link on the very bottom of the left side panel. It is not very noticeable, and it is not evident on the first glance that this image has parents.
I think it would be better to have such link at the top of the page above the image, in the same way as parent image post.
Sorry for bad English.

Tweaked. :)