I found this image a little while ago.
It appears to be fan depictions of the magical girls who end up becoming witches who are fought in the series. I know that:
The 2nd one is Elly due to the the apperance of the screens on her left and the doll thing which is like Elly's Minions
The 3rd is supposed to be Nagisa looking more like Charlotte
The 5th one is Elsa Maria due to the appearance of the Sun above her head
However I don't know which witches the first and fourth girls are supposed to be.
the crests in the background are giving it away from left to right:
The 4th girl looks a lot like Gertrud. I'm not sure about the first one, however, as there are no witch that is associated with those weapons or her colors of the witches in the anime, which I assume the fanart is based on. There are also no witches from the manga spin-off that might look like her.
Adding to what Frosteeze said (I still can't add comments), the most left girl might be Gisela as shown from given link (http://wiki.puella-magi.net/Madoka_Magica_Characters). I think it might have to do with the crest behind each girl.
The wiki page on Gisela mentions that she's the silver witch, and the first girl clearly has a silver color theme. The wiki also speculates that the magical girl who became her was a bosozoku. The bokuto and nail bat that the first girl is carrying are associated with bosozoku. Whether or not this is true, the artist of the picture might have believed it and included it in the picture.
