Fading images

How can you fade an image in form left to right? I’ve seen it done on a few sites and I can’t figure it out. If anyone knows can you please post it here.
thanks

fade in, form 0% to 100%? you make of you image a mc and you go to alpa and their you put 0%

i hope that this is what you looking for

you can either motion tween a mask (which both eat up processors) -or- you can motion tween a shape (like a rectangle) that has a custom gradient.
One side of the gradient is a solid color the same as your background and the other side is a custom color with a 0% alpha.
-Cheers