Looking at how cover images can be handled within the peeps section profiles. Looks like on my screen they can go up to 1387 x 255 pixels. I am guessing people with larger screens and smaller screens may find the image size slightly different. Not sure if the images will be scaled or squished with different image sizes at this point.
The cover image uploader wants you to provide a pic that is at least 860 pixels wide, and at least 255 pixels.
It will auto crop a bit skewed towards the vertical center, and it may zoom and re-position as well.
This is a relatively new feature and will have additional options in the future.
Since we are using a dynamic / auto changing, expanding / shrinking design for this section of the web site, image sizing may vary.
I can modify these things of course, so the information as accurate posted today may vary in the near future.
if you upload based on the smallest image size possable (860 x 225) or what its displaying in the css of the peeps profile then it skews them, or more specificly it displays at the proper size but the image is actually blown up and cropped. the percentage is actually rather large, i havent sat down and booted up a test but i woul say it probably enlarges it 100% then crops.