There is no "grey" area
When it comes to the desire for food, a person always has that "grey" area of deciding what he should eat--for his bodily strength, and what he shouldn't eat--either because it's not healthy for him or because it's too much. However, when it comes to "lusting" for other women, whether through pictures or in real life, there is no "grey" area. It is plain and simply "bad" for you.
The entire "lust" phenomenon was created by G-d to bring a man and women together for the purpose of building a family. Any other type of lust which is not for the purpose of marriage, and especially if one is already married, is very, very unhealthy, both spiritually and physically. It does nothing besides destroy people's lives and take them away from G-d and from their goals in life.
Therefore, don't be afraid to just give it up to G-d. Just say to G-d with feeling, "Dear G-d, I truly want to give you this habit of lusting, - even if it means ripping my heart out! PLEASE. Take this "lusting" away from me. I want to give it up to you G-d, for the rest of my life, as a true sacrifice. For I know that you G-d, are the true source of all beauty, all love and all desire".