Credits do not appear

What options do you have on the settings page? Can you post a screenshot?

I have tried all three of the Display Credits options (before the content, after the content, and overlay on images) and none of these have worked.

What do you need a screenshot of?

a screenshot of the plugin’s option page and the page on the media library where you specified the source and link for the image

Will these work for you?

https://drive.google.com/file/d/0B3sz_tyFzC_MSG1jU2ZHcThMN28/edit?usp=sharing

https://drive.google.com/file/d/0B3sz_tyFzC_MeWtaRGVEaWcteVU/edit?usp=sharing

Perfect,
Do you know if your theme is using get_the_post_thumbnail or the_post_thumbnail to output the featured images?

Can you try inserting the image directly in the body of the post?

My child theme uses the_post_thumbnail().

And for your second question, I’ve added images using the Add Media button.

the problem is that the plugin relies on the image having class wp-image-<id> which is normally added when you insert the image in the post. Here, your image doesn’t have that class which is probably filtered at some point by your theme

Thank you for the information. I did indeed test it with the Twenty Thirteen theme (again) and Twenty Fourteen, and everything functioned properly. I will have to look further into this, for my theme.