Bloody Glowing Eye

Get the original pic here.

First thing's first, we're going to add some roughness and cracked skin.  So find yourself a picture of leather, preferably one that is as large or larger than your eye image so we don't lose any sharpness through resizing.  You can also make it larger by duplicating it and edit > transform > flip vertical or horizontal, move it around until they fit and then select both layers, right click them in the layer menu and choose merge the layers.

Set the layer blending mode to multiply, and drop the opacity to 70-80%.

In my case, since my image is black and white, I went to image > adjustments > desaturate, but if your main image is in color then you might want to go to image > adjustments > hue/saturation, to keep the color but help it blend in more with the image.

Using a medium-sized eraser with 0-50% hardness...reducing opacity where needed...erase the leather from the eye, background, and anywhere else where it looks inappropriate.  Merge the background and the leather layer.

To make the eye glow, I chose to use some excellent free brushes, which you can pick up here.

Take a nice bright red, start with the most round brush, and plonk it right in the center of the eye.  Take a soft eraser and clean up anything that falls out of the eye area.  Reduce the opacity to 50% and the layer blending mode to lighten and repeat the process, using a different layer for each brush stroke and changing the color, layer blending mode, opacity, and brush type to add depth and variance to the eye.  I chose yellow and an off-white as my highlights to the red.

Find yourself an image of veins...leaf veins work well, which is what I chose to use.  Paste it on top, resize it appropriately, and rotate it to fit the direction of the eye.  First we're going to get the color right by going to image > adjustments > hue/saturation and fiddle around there until you're happy (sometimes selecting colorize, even if it's already colored, can have an interesting effect.).  Duplicate and hide the layer to save for later (in case you want to add more veins).  Drop the opacity of your vein layer down to 50%, and if you need to, you can go to edit > transform > and warp to make your veins curve around the eye more naturally.

Next, take a soft eraser brush and remove any veins that overlap anywhere but the whites of the eye.

Grab the lasso tool and draw the blood drip, then make sure you're on the background layer and copy and paste the drip.

Now to get a nice bloody color and keep the background texture, go to image > adjustments > variations and fiddle until you're happy with the color.  Go to select > reselect, then select > modify > expand and type in 10.

In the background layer, copy and paste this larger drip, make sure that it is behind the first one, and repeat the variations process.  Now reduce the opacity of that layer to 50% and merge the two drip layers.

Go to filter > blur > Gaussian blur and set it to about 2.

Grab the smudge tool and set it to 50% strength, 50% hardness and a mid-size brush (100px).  Use it to soften the edges, make them less rigid, and create a more natural flow.

Now we're going to dodge and burn some dimension into our blood.  Take the dodge tool and set it to Range: Midtones, exposure 50%.  I like to start with a relatively large brush (75 px) and highlight larger areas first.  Brush over anywhere were you think the blood will be particularly gloopy and the light would hit it naturally.  Try to follow the flow of the blood.  Next reduce your brush size to 40, exposure to 30% and set range to Highlights.  Use the brush to accentuate the areas that you lightened.

Switch to the burn tool and set your exposure to 20%, size 80, and range to midtones.  Firstly go over the outside edges of the blood to give it a more 3D look, then further darken sides where the blood is thickest or however looks most natural.

If you choose, you can make the blood extra glossy with a few subtle highlights, using a size 10 paintbrush, 0% hardness, opacity 50%, and paint a few tiny highlight stops with white.  Go over the spots with a soft, low-strength smudge brush to blend them in a little.

If your blood drip is a bit bright go to image > adjustments > hue/saturation and darken it a bit.

Finally, make a new layer, take the paintbrush tool and set it to size 100, 100% opacity, and 0% hardness.  Hold down shift, select a red color from the glowing pupil, and paint a thick line over the bottom and top rim of the eye, going straight over the blood drip.  Hold shift again and select a bright yellow from the pupil.  Paint yellow over the red in areas where the glow would reflect.

Change the layer blending mode to soft light,  select the smudge brush, set it to a large size (200 px), strength to 50%, and smudge the paint so that it blends in well with the image.

And you're done!