just click on my smiley face...I think the min..is 15bucks, but honestly this forum has been more then worth the 30 dollars I donated...Its been a great resource, because my premed advisor sure as hell isnt
Option 1: (recommended)
Step #1, install Windows on your Mac
Step #2, choose from a plethora of programs that will allow photo editing/resizing
Option 2: (photoshop)
You say you have photoshop...just save it as a lower-quality file such that when you view file properties for the jpg it is <19kb. Then SDN should handle the resizing. But I don't see why resizing it to 100x100 in photoshop wouldn't work.