Did you know looking at your own post increases the number of times viewed for images on that post?

[NotRexButCaesar]

If you make a post with an image attachment, then repeatedly click on "Board index", and navigate back to your post, the attachment will count each navigation as a new view.

[Sanqui]

It's just phpBB's naive view count. I think it's mainly designed for attachments which you can download, where the download count makes a bit more sense. The informative value it provides for images is dubious, but it's there.