Torn Border

1. Create a new document, with a white background, and paste an image into a new layer within the document. Now use the Rectangular Marquee tool ('Shift' + 'M') to create a rectangle inside the image. Finally, press 'Q' and the outer borders of your selection will appear red (which means you're in Quick Mask Mode).

2. Click Filter > Brush Strokes > Sprayed Strokes, and enter a Stroke Length of 19, Spray Radius of 21 and for Stroke Direction you can pick anything.. (i left it default), hit Ok, now press 'Q' once again on your keyboard to exit the Quick Mask Mode.

3. Press 'Ctrl', 'Shift' and 'I' to inverse your selection, then hit Backspace.

4. To get a black background, or anything other color. Go to your first layer (should be blank white) and just change the color of it to another.