Typically just providing a note RE image sourcing at the bottom of the post would be sufficient here e.g. a note that you have permission to use these images from Blue Osa and a link to flickr or someting like that.

Not sure how you were attempting to provide sourcing but the post editor here is a little... lacking in functionality (to put it kindly) and a lot of HTML doesn't work in particular. I didn't look at your source code to see what you were trying to do.

Cheers - Carl