It’s much easier to do this in Photoshop, but if you don’t have it then this is a fairly simple way to do it in PSP.
1. Open up the image you want to use in PSP. I would recommend a large image, since this tutorial is great for making backgrounds, but it’s up to you.
2. Make a new image that is the same width as the image you just opened, but a lot bigger in height (I’d say about 400-600 pixels bigger, depending on the size of your original image). For example, my original image is 283 x 228 pixels, so I’d make the width 283 and the height 400. Make sure it has a white background.
3. Now copy your photo, and then click your white image and press Ctrl and L to paste as a new layer.
4. Move your photo image to the top of your white background, like this:
5. Now click , and if your Tool Options box isn’t up then right click and click Tool Options. Change your settings to match mine:
6. Go to View > Zoom in by 1, and click near the bottom of your image and drag the cursor all the way across to make a small rectangle only 1 or 2 pixels high. See mine (zoomed in):
7. Then copy (Ctrl and C), and paste as a new image. Go to where you change the colours you want to use (colour palette), and select the Patterns feature (shown on the image below), by clicking the tiny black arrow and then the dotted square.
8. Find the pattern you just made, and go back to the image you selected a bit of before. Press Ctrl and D to deselect, then click the Floodfill icon, and click the white background on your image. Then, just save!