Tarbat
I believe it is the way it is because of the ANet T&Cs. ANet photos are not free to use. You must either use links or individually gain permission from the photographer. Airnav chooses the former option
http://www.airliners.net/usephotos/"You may not use these photos on any web page, commercial or non-commercial, for profit or non-profit, without written permission from the photographer. You may however link to the photos in the manner described below."
"Finally, we ask that you mention Airliners.net where and when you use photos originally found on our site, whatever agreement you have with the photographer. It doesn't need to be big, just a small mention in whatever way you choose. As you might have realized by now, we do not make any money from selling photos, everything goes directly to the individual photographer. Our only form of "income" is your help in spreading the word about our website. Please respect that."
The Airnav software shows the thumbnail but credits the photo to the Anet photographer (PT fields) and links to the full size photo (LK fields) from the thumbnail. If you hover over a thumbnail it says 'Photo copyright by .......... Powered by Airliners.net'.
Of course at the moment the credited photographer is not the photographer from the thumbnail but of the background link. The photographer of the thumbnail therefore goes uncredited due to the bug.