BIRT relies on the Qt library for its image handling. As such if the installed Qt library doesn't support the image format, neither will BIRT. The version of QT used to build this instance of BIRT (%%QTVERSION%%) supports: %%IMAGEFORMATS%%.
This should rarely happen with Qt 4.x as it was created post-2004 when the LZW patent expired. Without this patent there is no limitation on the use of GIF images and so Qt defaults to including GIF support.