You're doing well to still fight this despite the obvious urges, but for the temporary release self harm gives, it is not with it to cave in when the permanent damage is so obvious.
Cutting is so often a coping mechanism, a form of release, a way of making internal feelings physical. For these urges to become less frequent and strong you need to address what it is you're really feeling.
Address what event happened that day to make you start to have these feelings... A bad day at work or school, a row with a family member or just depression in general. But you need to deal with these feelings instead of using self harm to deal with it instead.
If you haven't got support from a doctor I would suggest you do. Talking is a big help, although it can be hard for a lot of us here to voice our feelings and opinions.
How long were you a cutter? If you haven't started and they just come to you- see a doctor. If you're trying to quit, withdrawals. Mostly it's just stress and a sign that you need to see a doctor or speak to someone. Each day will get darker and darker until those images won't be images and by then it's harder to prevent it from happening.