Envy is a very complicated sin, it's not as objective as all the others really and generally everyone in their life is going to feel envious of someone who is better off then them at some point in their life. Envy is a sin in which I myself am guilty of, there have been moments in which I have been alone and seen other people kissing in public and yes I try to think 'hey good for you two' but I cannot help but feel 'you lucky bastards'. Envy tends to be a by-product of loneliness and that appears quite apparent with this piece as well. The sinner alone ultimately looking to the mirror and wishing things were different, a place we have all found ourselves at or will find ourselves at in our lives. Envy is a sin very few can live without experiencing, because it's a very subjective state of mind. Be that as it may it is presented in a very familiar and ultimately sympathetic way.
Gimp should run the same way? (I haven't used it in a while, but they are similar programs and gimp is free). That's okay, not a lot of people understand all of photoshop who have it, so I expect you wouldn't know much about it.