Nice find!
At the top of the page it shows it was uploaded by gadl. In this case, it appears there are no special notes. this is what creative commons suggests.
http://wiki.creativecommons.org/FFAQ#How_do_I_properly_attribute_a_Creative_Commons_licensed_work.3FOn that page there is a bullet point that I think answers your question.
If you are making a derivative work or adaptation, in addition to the above, you need to identify that your work is a derivative work i.e., “This is a Finnish translation of the [original work] by [author].” or “Screenplay based on [original work] by [author].”
jagguy, Your original question was asking where to find free photos. I trust that you have now found some good sources and can close out this question.
As far as how specifically to give attribution, you really should be asking your lawyer.
If I was doing this for a website, I might attribute something like Photo by gadl where I place a hyper llin on gadl that links back to
http://www.flickr.com/photos/gadl/89657946/sizes/m/ I might also go so far as to take a screen shot of the page with the creative commons license for my own protection. After all, gadl could very well be uploading somebody else's images. In your case, it sounds like you are making a desktop application and unlike a website, you can't just quickly remove the image from all of your distributed applications.
It is good you are being cautious and not using just any image. I think you are finding it is going to take some time to get good free images for your project and that is why I suggested earlier it might be worth spending just a little bit of money and getting everything you need much quicker and you will have a more clear license.
