what causes "grainy" pictures?

[xxmichellexx]

I am in no way a photography expert (or anywhere close to it), so please bear with me. My previous camera was a point & shoot Kodak Easyshare which took good pictures and was simple to use.

I recently bought a Canon Powershot S3 and I'm having problems with pictures even on the "auto" setting.

This is a picture I took this morning:

http://img.photobucket.com/albums/v68/babytex/March%202007/2007mar27b.jpg



And for a comparison, here is one from a couple days ago - same subject, same room, same camera settings, just a different time of day:

http://img.photobucket.com/albums/v68/babytex/March%202007/2007mar24b.jpg

I am still trying to learn how to use the camera on even the most basic settings, but it seems to me a picture shouldn't look like that (the first one) if I did everything right. If I have it set on auto and use the flash when it tells me to, what's the problem? Was it too bright in the room? Too dark? Should I change something on the camera?

HELP!
Thanks.
Michelle

[JLV]

It was probably taken at a high ISO.

[David Metsky]

In auto setting the camera will choose to push the ISO up high when the light is low. Did the first image use the flash? High ISO (400, 800) will be grainy.

You can put the camera in Manual or Program mode and select the ISO. If you want to avoid grain choose 80, 100, or 200. Anything higher then that will probably start showing grain. In low light you'll need the flash, or use a slower shutter speed, but that will lead to blurry images if your child is moving around.