Okay. apparently, the largest the pic can be is 75 pixels by 75 pixels.
My suggestion is to download the wonderful freeware program XnView.
Then just copy whatever image you wish, click File-Import Clipboard, then click Image-Resize.
The pixel size for Height and Width will appear before you.
XnView just keeps the picture proportional, (unless you manually change the setting), so just write in 75 pixels on the larger dimension, save the file, and you should be all set.
PS: When the XnView screen come up, there will be a big section of Program Files or whatever folder you keep pics in come up on the screen. Just "X" out of that and you should have a nice, gray, blank area for your pic to appear after you click "Import Clipboard".
PS: I suggest you save the pic as either a GIF or jpg file.