I believe all of the CC licenses require attribution, so you should be fine with any of them in that regard. However, from my understanding, attribution is naming the photo's author, so it's a slightly different issue than placing a URI with the image.
You simply may not be able to control the URI (if one is even used) that the user specifies. From my understanding of the licenses, CC doesn't require the use of a photo owner's requested URI if it's not "the copyright notice or licensing information" or if it isn't "reasonably practicable" as they put it in their licenses.
This might be why Flickr and CC is slow to respond about this.
All that aside, I want to make sure our service is a great thing for both photo owners AND bloggers/website owners, so I appreciate you bringing the issue to our attention. Perhaps we at Wylio can figure out a better solution to the issue than has been used in the past.
Thanks again for contacting us, I hope I've been helpful!
-Dan
to the extent reasonably
>> practicable, the Uniform Resource Identifier, if any, that Licensor
>> specifies to be associated with the Work, unless such URI does not refer to
>> the copyright notice or licensing information for the Work;
Hi Dave,
Attribution and URI requirements are listed separately in that CC license. The "human readable summary" you've linked to doesn't get into the details but the full license does. See my previous messages for the applicable excerpts.
You can find a link to the full license at the bottom of the summary you're referring to in your previous message.
-Dan