Try this link, after clicking this you should get redirected to a website where you can paste your long link and click "shorten link" and then copy the link and use it here. No pun intended(this very long link (lol)
As in the pixel size? The only way I know of how to change that is to go through certain websites to change the photo dimensions for you, or upload it to photobucket with your upload settings set to a certain size.