Adding long hair to pictures is simple if you have a powerful image processing program, such as Paint Shop Pro. The trick is to use the clone tool, which allows you to use a part of an image as if it were a paint color. In any picture, hair is just a mass of color and texture which can be easily reproduced and worked in to seamlessly blend with other areas of hair.
Gather together several pictures which were taken on the same day and in the same lighting conditions. Scan them all into your computer, or download them from your digital camera.
Import the pictures into Paint Shop Pro by clicking the browse button, which looks like a file cabinet. Then click the clone button, which looks a little like two people joined by an arrow going to the right. Open all the pictures which you scanned or downloaded. If you're planning to work from the same picture, save the picture using two different file names. Open both copies of the picture in Paint Shop Pro.
Find an area of the hair that looks like it's flowing in a downward direction. Right click on the copy of the picture which you intend to leave intact. Left click on the destination picture, and begin to paint the hair in, carefully watching your source picture to avoid getting outside of the hair boundary. If you do overstep the hair boundary slightly, however, it can be fixed later by cloning in the proper texture for that area.
Add some hair volume in different areas so that the two masses of long hair don't look like perfect copies of one another. One trick is to reduce the size of the brush in the Tool Options Palette, then draw the hair in strands. Try a few different things, and click Edit > Undo if they don't look right.
Right click on the original ends of the hair in your source picture. Use the clone tool to add these ends to the ends of the added long hair strands to make them look real.
Select the soften tool from the toolbar. Zoom in on the edited image with your mouse's scroll wheel and look for any area which seems to have a hard, harsh edge. Stipple over these areas with the soften brush. Do not attempt to drag the cursor across the sharp areas, as this will not have the desired effect.
Save your image with a new file name.