I've created a couple of groups now and no matter what I do the logos I upload for them look weird. And by weird i mean that they look zoomed in, as if I have uploaded a logo that was too big and ning cropped a square in the center of it.
I've tried several sizes. I've tried gif, png and jpg. same result.
I have even tried uploading a version that is smaller than the actual logo space (approx 110px width). But then ning stretches my logo so it still seemes zoomed in!(and now pixelated because it was originally smaller...)
Se a photo example. The logo is supposed to read "K" and "Kawasaki"
The picture needs to be as close to a square as possible, because what it's doing is finding the largest possible square area it can, and cropping the rest. I'm not sure what size ning resizes the pictures to, but I have not noticed any loss of quality by making them 300x300 or bigger (bigger is fine. If it's too small it loses quality by being blown up)
I tried to see if I could figure out a solution for you with Paint (no luck), but do you have any Adobe design/photoshop applications or any software like that? If so, for this photo you'll want to change the height on the canvas size to equal the width (turn off "constrain proportions" first), use the fill dropper to match the white bg on your logo, and fill or put a box that color behind it. Voila, you have a square!
However, for things like photos and more complex backgrounds, you may have to go the route of manually creating at least a 300x300 canvas, and then pasting the pic over and postioning/scaling it manually (shift to scale down as you resize on adobe). By the way, this would be a nice feature from Ning, like they allow you to manually do with your profile pic on Facebook and Google +.
Those are about your only 2 options, and of course in some cases an oblong or skinny pic/logo just isn't going to work no matter what you do.
(P.S. If you don't have one of those programs and you just have a couple you need done that are that easy, I got a few minutes to help right now if you want to PM me instead)