Fireman - a scanned photo is a continuous tone image.  
"	Jpg works better than gif in compression; 
o	it is the format designed for photographs
o	it compresses using algorithms, which yields smooth shifts in color changes
o	At 10% quality, the image is pixilated - has big blocks of colors, with few gradations
"	Gif compression does best with colors in long continuous horizontal paths 
o	it uses run-length encoding; hence takes longer (and creates a larger file size) with complex images
o	compression is done by reducing the number of colors per pixel

Fish Bowl - an illustrator image that is a hybrid, combining line art & continuous tone
"	What works best may depend on what's more important - small size and fast speed, or higher quality; it's a trade-off	
"	Gif works best with this image if speed and size are most important;  the number of colors can be reduced, and hence the file size can be smaller
"	Jpg works best if rendition of the gradations of color is the more important variable; the file size will be larger than a gif.

Marin Logo - an Illustrator image: example of line art with gradations; hence, a hybrid
"	Jpg works best for this image; the gradations of the sun are hard to compress with gif
"	BUT - gif can get an acceptable image with 256 colors, and results in a smaller file size
"	Dithering does not help, and adds to the file size

Jack in the Box - an Illustrator image made of solid colors
"	Gif works significantly better than jpg for this image
"	The number of colors can be easily reduced to 64 - and even lower by locking in individual colors; this results in a much smaller file size than jpg
"	At 32 colors, the gif image has jagged lines (artifacts) around the green ring, and the colors shift considerably.

Barney - line art: two colors only (black and white)
"	If you resize this before converting it to grayscale, the file size is significantly larger (149 vs. 50); but, Image Ready only works with RGB, so you can't use the Save for Web option unless you convert back to RGB, which brings the image size back to 149. I can't see a quality difference.
"	Colors can be set to 2, but the quality is insufficient; 8 works better.
"	Dithering makes no difference (not enough colors to dither!)