All of these album colours have dark colours, which is typical of a rock album cover. Also, all of these album covers represent the darker side of life, ie, The Devil’s Got A New Disguise features a skull containing 2 children drinking alcohol, The Open Door features Amy Lee, the singer, walking from a shadowed area, Only One features a picture of a man’s face with part of it missing, Dethalbum 2 features an evil mermaid and Silver Side Up features a pictures of an eye with tears falling from it.
Another way of distinguishing the genre of the music video is to look at the font style and the colour palette. All of the album covers contain black and many other dark colours, mainly dark blue. The font style of Only One and Silver Side Up is black and bold, whilst The Devil’s Got A New Disguise has got a rune-istic quality to it, and the colour of this writing is white. The Open Door is the band’s writing, therefore showing that the band has a say in what goes on the front cover of their album and Dethalbum 2 also has the band’s font of writing, showing furthermore that the creators of Dethklok had a say in what goes on Dethklok’s albums.
I think the idea of album covers are to help promote the genre of the band, by showing what the conventions of the genre entails. It is also a conventional way to make money, by selling albums, singles or digipacks, which features exclusive extras, including DVDs and posters of when a band was recently on tour.