Can thumbnail pictures from Jetphotos.net and Airliners.net be (legally) used as an avatar here? I had a couple of shots that I liked but wasn’t sure about doing it legally. If not, where could I get some that are legal?
Note: My current avatar was a self-made image.
You answered your own question in your note.
Standing by for the followup question. 
There are a lot of great aviation photos on Flickr. Unless otherwise stated, they are available for your use. http://flickr.com/creativecommons/
In the “fine print” of the above under attribution.
" but only if they give you credit."
To play it safe, somewhere should be credit in the Avatar or description in the “location field of these forums” giving credit to the photographer for the photo is the way I read it.
Just to add my 2 cents: The avatar has to be, what, 80 x 80 pixels? The creative commons page states “No Derivative Works means:
You let others copy, distribute, display, and perform only verbatim copies of your work, not derivative works based upon it.”
To me, reducing the size would be a derivative.
What does it mean in everyday life about using airliners.net or jetphotos.net? It would be illegal but the chances of getting caught would probably be slim. The original photographer may not even recognize his photo due to the reduction in size and cropping. However, I wouldn’t create an avatar out of photo from either of those sites because the pictures are copyrighted.
Why don’t you find a picture you like, create an avatar, and then contact the photographer. Show him the avatar, explain where it will be used, and then ask permission to use it. Unless the guy is really a hard head about it, you probably would get permission. I know I’d allow any picture of mine to be used if the above procedure was followed.
RE: Flickr
If they don’t select creative commons you can use it, the picture is in the public domain. People have had their pictures show up on cell phone billboards in other countries and there’s nothing they can do about it.
Do you have a link to support this? (bolding my emphasis)
As I understand it, if you don’t select any of the creative commons licenses, then the picture is fully copy right protected and shouldn’t be used without express permission of the owner.
Picture being on a public domain website is not relevant to copyright issues based on all that I know.
Yahoo terms of service wasn’t of any help as it only addressed posting pics on Flickr, not the usage of pics from Flickr
Should have read a little further down on the page. There is an option for non-commercial:
Noncommercial means:
You let others copy, distribute, display, and perform your work - and derivative works based upon it - but for noncommercial purposes only.
This could mean that you are allowed to make an avatar out of a picture without attribution.
I tend to agree with Wazzu90. Looking through the terms of service, I would say that if you don’t claim a copyright then the pictures are in the public domain.
I got my avatar from airliners.net. I simply contacted the photographer thru email (there’s a “contact” link for each photo) and explained that I just wanted to use the image as an avatar on an aviation Web site. He replied rather quickly and gave me the green light.
My apologies for the double post - I meant to edit my post above and created a new reply by mistake. 
As I posted earlier, by default photos are copyrighted as soon as the shutter button has been pushed and the picture recorded…
In order for it to be public domain the photographer has to explicitly say so.
Posting to Flickr does not relinquish the copyright to the photo you took, the common creations just allow the photographer flexibility to assign the usage of their photographs which can be changed at will (or midstream) by the flickr account owner. The photographer still own the copyright to the photo.
templetons.com/brad/copymyths.html for a factual reference.
Simplest solution is NeedleNose’s suggestion. Just contact the photographer. Problem solved.