Open up your picture in Photofiltre and a new blank image document.
If your picture is too big, resize it to a smaller size.
Now using the selection tool on your picture make a selection around the part you want to put in the Polaroid or just copy the whole thing.
Paste it into the blank image by pressing Ctrl-V.
Press Ctrl-D once.
Now go to Selection >> Expand. If it doesn’t give you the option of Expand, click Ctrl-D again. Make the radius whatever you want. I made mine 10.
Now on the selection line on the bottom, move it down a bit farther.
Press Ctrl-C and then Shift+Ctrl-V.