Well, first of all I think it's a great idea to show the release type on thumbnails!
But there are two things, that I would change:
1) Colored circle
I think the colored circle, which is used as a background, does not belong here - it really does not fit in.
I would replace it by the same background-style, that is used in the other corners.
2) Single character
Since there are two "pre-defined" release-types starting with "A", I would switch to show the first three characters ("Album" -> "ALB", "Anthology" -> "ANT")
Also I don't know, how the characters are selected for custom release-types:
"Remix-Album" -> "P"
"Tribute-Album" -> "P"
"Charts" -> "M"
Possibly it's even better to avoid to use the three first characters and instead just let the text be trimmed when to long.
This would most likely allow texts like "MAXI", "ALBU...", "LIVE"
Might be important for users which are using custom release type names?
It should be I think, I wll do some further tests.
This is how it will look. I expanded the width of the overlay so that it could show more info.
It it is too long it will have trailing punctation.
Seems to work quite well:
It was a bit worse with the file-type so I will leave that one as-is.