Images in Optio depend on the version of the software and on the device you use for it.
the pcl device only supports monochrome (1 bit color) images, gif's will be made monochrome in a bad way. the Postscript devices support colour images when you have setup a pallet in the device. The GDI device (windows only) supports all colours, and the printer will work it out. The PDF device devices support colour images.
in Designstudio 1.x (ODCS 6.x) you can use tiff, gif, png, and bmp images with DesignStudio 7.x and eCI you can also use JPG.
tiff images can be compressed in several different ways, optio does not support all. but if you make them 300dpi uncompressed 1bit color (2 colours) you will get a perfect image. (yes it is big, but as the image always will be converted to the printer image format, this does not matter in the end). You can put images with different dots per inch settings but this will sometimes create a Moiré pattern effect.
Using gif or png image format can sometimes (especially if you use colour in a black & white output like PCL) give a blotched appearance due to the way the image is converted by eCI.
To convert images to any particular format you can use Imagemagick (all platforms) or Irfanview windows only.
When you use a lot of images (and i mean hundreds) on a windows server in one spoolfile, the serverprocess might choke and die.
