It seems that MoveableType doesn't recognize my favorite file format, .png. Fortunately, adding this capability is very simple.

I'm using NetPBM for image manipulation.

In mt/lib/MT/Image.pm, find the line:

my %Types = (jpg => 'jpeg', gif => 'gif');

and make it:

my %Types = (jpg => 'jpeg', gif => 'gif', png => 'png');

That's it!