Use original format for thumbnails/resized images (same as the image)

[Aleksej]

Resized versions of an image need to be in the same file format as
the original, or at least in a format which has the required
features (e.g. transparency).

The logos of Creative Commons recently uploaded by fajro to omgmg
have bad thumbnails, because the original images are in PNG format
with transparency, while the thumbnails are JPEG. The
black-on-transparent logo became black-on-black, and the
white-on-transparent logo became white-on-white.

[Christopher Allan Webber]

This is actually a really easy bug if someone wants to pick it up.
In fact, I think all you have to do is remove the explicit convert
to jpeg calls that are currently in there, and maybe also manually
set the extension of the filename that's pulled in?

[Inconexo ø]

On my copy no conversion is made. I uploaded a png, and it gave me
a png thumbnail.

[Christopher Allan Webber]

Oh yes! I changed this and forgot to mark it as done :)

[Will Kahn-Greene]

The original url for this bug was ​http://bugs.foocorp.net/issues/594 .