There is a utility called GrabIt that ships with the Mac. Pull up the pic and use GrabIt to capture the window that the pic is in. This will save it and all you need to do is open the new file with Preview and SaveAs a jpeg. There are other more streamlined methods, but this will work in a pinch.
Wow. deja vu
If the pic is too large, Preview will fix it. Just select the menu command to edit the size and type in whatever size you need. Save that one and post it. I try to stay in the area of 100. Give it a whirl.