This stuff is my opinion after a number of years as an image-maker online. I don't think there's a gold standard anywhere or a law that the Internetz Police will bust you over.
- Go beyond Google Images or Wikipedia to the original photographer, illustrator or artist.
- Check for a Creative Commons Licence*.
- Ask. Just ask if permission is unclear.
- Credit the photographer, illustrator or artist by name.
- Link back to their site.
Saying "Credit: Google Images" is like saying "Credit: Someone on Earth".
If you search for more than 10 minutes online and cannot find the original creator and are desperate to use that specific image, perhaps put it up and ask your readers for help identifying who created it. A knowledgeable blog readership on a niche topic will often know.
Be prepared to take an image down if asked.
*A note about Creative Commons Licences: it means some sort of sharing is allowed, but the most restrictive licence still says a) You must credit the artist b) You must not alter the image in any way and c) You must not make any money from it. It's one of the reasons an artist may allow free use on a blog, but ask for money if it will be in mainstream media.
These are my opinion on the subject of credit: thoughts?
- - - - - - - -
under Creative Commons Licence.