If you need to crop black border, it is better to capture in PNG, remove borders, then either save to JPEG (if you can set the compression/quality level) or keep the PNG and let the site do the compression.

To remove the borders, I use XnView, so I can do a batch-update of the images and remove the borders on all of them at once (I check on one image what are the coordinates of the useful part, and then I crop & resize all pics with the same parameters).

PS: I've split the discussion from the "Site updates" thread, as this was not really related to it.