We all agree with Robin Good that this is a "good guide providing the basic principles that should be followed when using, reposting, citing or quoting other people's content (both text and images)".
Crediting images is something that has been forgotten but it deserves the same attention as written documents.
The article is very complete, covering the topics:
How To Cite Content in Blog Posts;
How To Cite Content in Social Media;
How to Give Credit to Guest Bloggers and Ghost Writers;
How to Cite Images and Visual Content.
Those are premisses that also apply when curating content for whatever purposes.
Via Robin Good, janlgordon, Dennis T OConnor