Melanoma on skin in bruise form, what does it look like? (photo)

I've seen online pics of melanoma as a mole. However some sites say it can be on skin as bruise and not part of a mole. I have dark patch that noticed 3 weeks ago. Skin is dry there and itchy sometimes. I plan on seeing dermotoligst this week. In looking at picture attaches could melenoma look like a dark patch like I have on my back (upper LEFT)? I realize it can't be diagnose online from pic but from the look of this should I be concerned?