Prior to version 1.30, you could only view images stored as gifs or bitmaps. As of 1.30, you can view any image file with one of the following extensions:
gif
bmp
jpg,jpeg
png
tif,tiff
xpm
xbm
tga
sun
sgi
ps
ppm
pixmap
pcx
ico
Of course, the data inside the file has to be in the format implied by the extension.
How do I view a chart stored in a particular raster image format?