Found a solution that can be used to enhance Celestia very much.
A library that supports a lot of image formats (JPEG, JPEG2000, TGA, PNG, TIF, BMP, RAW, PNM, PPM, PGX and even MNG) written in C, open-source and licensed under the BSD licese.
A few days ago, version 1.3 came out.
Have a look at OpenJPG:
https://www.openjpeg.org/
If someone knows how to include and utilize this in Celestia (And using Visual Studio 2008 Express Edition),
please post a topic in the Celestia Development forum or post a reply under my message.
(I know VS2008 will be used after Celestia 1.5.0-1 this isn't a little change and can wait a little)