#emda340

What's an acceptable way to attribute the work of somebody else? In the case of creative commons, the original author is responsible for providing a preferred method of attribution. If you can't find one of these then I recommend attributing the original artwork with a modest watermark or caption. Every work licensed through Creative Commons (CC) requires attribution. Please take note that there are "NoDerivs" CC licenses that prohibit modification of the original work. This this wiki article sums up CC attribution nicely.

If the work is non-CC and you've worked out an agreement with the originator to reuse the work with attribution then there is no amount of modification that gets your off the hook when it comes to attribution.

From the Copyright.gov Fair Use Faq:

Only the owner of copyright in a work has the right to prepare, or to authorize someone else to create, a new version of that work. Accordingly, you cannot claim copyright to another's work, no matter how much you change it, unless you have the owner's consent. See Circular 14, Copyright Registration for Derivative Works.

If you've purchased the image from a royalty free service then you are allowed to modify as much as you'd like without attribution. If you've purchased usage rights from the stock imagery service then it's quite likely that you've paid for these rights by purchasing the work through the vendor.

The question remains: How can you properly mark a work so the original author does not appear to get credit for your modifications? You are allowed to have copyright over the portions of the work that are your particular contributions. You are more than welcome to reflect this in your markings on the image so long as you include attribution to the original work. So an example of this may be:

Animation and App ©2013 Randolph Jones, Illustrations © 2012 Jane Doe, Story ©2011 Imagination Stage

When using CC licensing take note that there are "Share Alike" riders on certain licenses that require you to use the same license on derivative works.

Again, for more information on the proper marking of Creative Commons content, this wiki article sums it up nicely.