Photoshop CC isn't just for making fashion models look perfect -- you can use it to add all sorts of interesting effects, including realistic scars. The process involves painting on a scar, giving it some texture with Bevel & Emboss and then blending it into the photo using Photoshop layers. To add your first scar to a photo, select a medium sized image with good resolution, like a headshot that's about 600 pixels wide. Anything smaller will make it difficult to add a scar, since you need some really small brush sizes for this effect.
Open an image in Photoshop and zoom into the area where you want the scar to appear.
Click the "Set Foreground Color" icon in the toolbar. Type "984A48" in the "#" menu. This is a dark grayish red that will be the foundation of the finished scar. You can get a similar color by clicking on the person's mouth with the Eyedropper Tool.
Click the "Brush Tool" in the Toolbox while "Layer 1" is selected in the Layers panel. Select "Dissolve" from the Mode menu in the Options bar. This will make the brush strokes dissolve into the pores or wrinkles of the skin. Change the "Flow" in the Options bar to 50 percent and leave the Opacity at 100 percent. Choose a thin brush size in the Options bar that matches the thickness you want for the finished scar. Six pixels should do well for a medium-sized photo.
Drag the brush across the skin where you want the scar to appear. Make sure you follow the natural contours of the body. If you're drawing a scar on a cheekbone, for example, the scar should normally be curved. At this point, the scar just looks like a crayon mark.
Add some stitch marks if desired by reducing the brush size to two or three pixels and draw them at about 90-degrees from the scar.
Change the brush Mode to "Normal" and double the brush size. Change the Opacity to 50 percent and the Flow to 100 percent. Trace over the scar again. Don't try to trace it perfectly, since any irregularities on either side will help the effect.
Click the "Layer" menu, select "Layer Style" and click "Bevel & Emboss." When the Layer Style window opens, drag it to the side so you can see the scar and make sure the "Preview" option is selected.
Select both the "Contour" and "Texture" options in the Blending Options menu. Select "Inner Bevel" as the Style and "Smooth" as the Technique. Set the Depth to about "285" percent, the Size to "5" px and the Soften option at "0" px. This makes the scar look like a huge welt with a garish line in the center.
Change the direction and angle if needed. If the scar is on a face, leave the Direction at "Up" and the angle at "120" degrees. You may want to change this depending on the lighting in the photo and the placement of the scar. Click "OK."
Select the "Smudge" tool in the Toolbox to remove any pixelated corners on the dark line in the scar. Set the Strength to "50" percent. Use a light touch with the Smudge tool. If you overwork the dark line, it will later look like a smear instead of a scar.
Drag the "Background" layer in the Layers panel onto the "New Layers" button to duplicate it. Click "Layer 1" in the Layers panel. Select "Merge Down" from the Layer menu, or press "Ctrl-E," to merge Layer 1 into the Background Copy layer.
Click the "Opacity" menu in the Layers panel and drag the slider all the way to the left to make the scar invisible. Slowly drag the slider back to the right. At about 10 percent opacity you have a very faint, old scar. At anywhere between 30 and 50 percent, the scar will be very pronounced.
Select the "Blur" tool by right-clicking the "Smudge" tool in the Toolbox if the dark line in the scar still looks too pixelated. Drag the tool over the pixelated areas as needed, leaving the Strength at "50" percent.
Select "Save As" from the File menu and save the scarred photo as a new photo in whatever format you prefer.
To make a fresh scar, use a thicker brush stroke. Add an extra layer once your scar is finished and draw a 2-pixel, black brush stroke and suture marks down the center of the scar at about 30 percent opacity.