I use a Canon S500 digital point-&-shoot for my eBay pictures at its highest resolution. Then I load the image into
my computer and use Photoshop Elements to tweak the image automatically--something like Google's "I feel lucky."
It usually works out very well. After that, I prepare the image for up-loading to eBay.
One of the things, still in Elements, is reducing the image to 1600 pixels on the long side, which is eBay's
recommendation. eBay adjusts the photo to whatever they like, and presto, nice picture and it always zooms up nice and large. Try never to enlarge a digital image—it just doesn't work out very satisfactorily.
Hope this helps.