We have been using the PhotoDropper plugin and it works great except for one issue.
When we set an image to be the featured image, none of the attribution options work. No attribution is displayed. We tested putting the image into the post directly and then the end of post attribution option is the only one that works.
I dug into the wp_database and there is some sort of attribution information in the post metadata. I can't tell how it is encoded, or how to display it. Right now our theme calls post_excerpt to get featured image captions due to the fact that WordPress handles featured images by making them "posts".