when syncing my iphone4s to my Mac it opens and starts downloading ipictures

If you don't want iPhoto to open when you attach your phone do this:

Attach phone

open Image Capture select your phone in the list on the left

At the bottom left of the screen is disclosure triangle click it

In the dropdown box select what you want to have happen when you attach the phone. If you want no applications to open select that.

Quit Image Capture