You can duplicate a photograph as many times as you would like, preserving the original copy while you draw on or otherwise manipulate the copies. Whether you want to add annotations, highlight important parts of the photo or add conspicuous mustaches to each individual in the picture, you can draw on photographs via your Mac using graphics-editing software. Some software, such as Photoshop, requires you to purchase a license, while others, such as GIMP and Seashore, are free.
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Download and install a photo-editing application like Photoshop, GIMP or Seashore (see Resources).
Start the application. Click "File," then "Open" and select the photo you want to draw on.
Determine how you want to draw on the image and select the appropriate tool. Do a tiny edit, such as more eyelashes, for example, with the "Pencil" tool; use a larger brush for more extensive edits, such as a Fu Manchu mustache. You can also use a USB graphics tablet if you have one; simply plug the USB end into your Mac, then move the pencil across the tablet to draw.
Click "File," then "Save As" and enter a new name for the photograph, then click "Save." This creates a new image with your drawings on it, preserving the original for later use.