Open paint, start making your sig. Open paint a second time and load the photo. Cut around the bit you want, and copy/paste it into your sig on the first copy of paint you opened. Then resize as needed for what you want.
I actually made the basic layout, copied the box onto the photo I was taking a bit from, then put it around the part of the photo I wanted, before copy/pasting it back to the sig. Its how I got all of them the same size
I also made my pawprint away from the sig, then resized and added to the sig, just pasting a lot of times to get the number of pawprints I wanted.