This is an example of a transparency using GIF. If you look close, you can see a ring of whitish pixels around the image:
This is an example of a transparency using PNG. Notice that the quality is much better (in supporting browsers):
Be carful with PNGs, however, because not all browsers support them properly. See the PNG transparency test for a comparison of browsers.
These are the various options for the CSS rule vertical-align:
Lorem ipsum rem "baseline" 
ipsum
dolor sit amet, consectetuer "sub" dipiscing
elit. Praesent lorem justo, consequat vel, eleifend quis, adipiscing at, risus.
Cras aliquam, magna et faucibus aliquet, tellus velit egestas metus, a "super"
consectetuer
arcu turpis semper dolor. Sed "top" risus
enim, gravida ut, vulputate at, porta a, mi. Proin tincidunt, purus vestibulum
nonummy scelerisque, sem libero aliquet dolor, eu adipiscing purus nisl "text-top"
vel
purus. Etiam interdum "middle" egestas
dolor. Nunc malesuada "bottom"
orci sed enim. Duis purus elit, blandit id, euismod id, porta convallis, lorem.
Sed volutpat nunc vitae mauris. Vestibulum venenatis. Cum "text-bottom"
sociis
natoque penatibus et magnis dis parturient montes, nascetur ridiculus mus. Nullam
vel nibh eu eros ultricies auctor. Proin id neque non ipsum viverra condimentum.
Pellentesque lorem metus, ultricies vitae, facilisis in, aliquam vitae, mi.