A tattoo scab on a healing tattoo (source)
During healing, some tattoos will form a protective layer of skin which will then peel away, and others will form a scab - it's completely normal, and depends on your type of skin, the way the tattoo artist's worked the skin, and your aftercare regime.

Don't Pick At It

During the healing process, your new tatto may become very itchy, and scratchng the area will be very tempting, but this can damage the tattoo as it may draw the fresh ink out of your skin. Slapping the itching area will cause a sting and the itch goes away. In some cases the scab that forms can become thicker and thicker as the days go by, and you may want to pick some of it off to see what's happening underneath, but this again will cause problems, so just leave it alone and wait. Thick scabs can sometimes be formed as people over-apply moisturiser or aftercare products to their healing tattoo. What seems to happen is that a small scab forms, and moisturiser is applied excessively - this turns the scab to mush, and then when it dries, it becomes larger and drier, so still more product is applied and the process repeats itself until the scab has grown very large. The best way to combat this is to apply the right amount of moisturiser from the beginning. Only a very thin layer is needed to moisturise the tattoo - any more can actually interfer with the healing process. So if your scab is turning to mush when you apply products - you're probably using too much. If a large scab has formed, try to be aware of it so that you don't accidentally pull it off your skin during the day, as it may degrade the image.

Cleaning

Scabs are formed from the dry blood and plasma which has leaked from the broken skin of the new tattoo. When cleaning a new tattoo, make sure to be gentle and try to clean all the blood around the wound to minimise the scabbing.

What if the scab comes off and my tattoo's blotchy?

If this does happen, and for any reason the ink comes out or appears blotchy, you can always go back to your local artist and get it touched up, usually for free, as artists are aware that the healing and aftercare process isn't a precise science, and provided you haven't abused your new tattoo, they'll usually be happy to re-ink it.