Flash photography commonly produces two flaws in photographs -- red eyes, which happen when the flash reflects off the blood vessels in the back of the cornea, and glass reflections, particularly in eyeglasses. GIMP, the open-source image manipulation program, allows you to correct these flaws with a variety of selection and repair tools. Using them in tandem, you can provide a natural-looking fix for low-quality snapshots.
Removing Red Eye
Open the photograph in GIMP. Use the "Zoom In" tools -- the magnifying glass -- to enlarge the face so the eyes are visible in detail.
Pick the "Fuzzy Select" tool -- the magic wand -- from the Toolbox. Set the "Threshold" slider in the bottom half of the Toolbox down to about 20. Then click the red portion of one of the eyes. The entire red portion should be selected; if more or less of the image has been selected, adjust the "Threshold" slider and re-click on the eye until you get the selection you want.
Select the "Color Picker" -- the eye-dropper -- from the Toolbox and set it to "Set foreground color" in the Toolbox settings. Then click on a dark portion of the eye, which will normally be a portion of the iris just outside the red area.
Click the "Bucket Fill" tool in the Toolbox and then click inside the selected area of the eye. The red is replaced with the natural iris color of the eye.
Correcting Eyeglass Reflections
Zoom into the face until you can see the eyeglass reflection in detail.
Select the "Healing Tool" -- the crossed bandages -- in the Toolbox. Move the cursor into the image, and you'll see a dashed circle at the point of the cursor. Adjust the "Scale" slider in the Toolbox until that circle is a little smaller than the reflection area.
Hold down the "Ctrl" key and click the cursor outside the eyeglass reflection, in an area where you can see the skin behind the lens.
Click and hold the cursor while stroking it over the eyeglass reflection. The reflection is replaced with cloned skin-tones from the area outside the reflection.
If your red eye photograph is a close-up, the iris may contain several shades of red. In this case, hold the "Ctrl" key while you click the areas with the Fuzzy Select tool. All the different areas of red will be included in a single select. Sometimes, the red eyes in a photo are so small that you can just paint them out with the "Paint Brush" tool.
This procedure for removing eyeglass reflections won't work if the reflection is hiding the eye itself. In this case you may need to copy the other eye -- assuming it isn't under its own reflection -- and flop the copied eye over its vertical axis. Then paste this eye over the reflection in the other lens.