The only dumb question is the one that's never asked.......
You cannot import graphics or pictures into FM3. All the artwork you see on the cars in the game was done using the livery editor. Unbelievable, I know, but true!
To get your pics online, you need to do a couple of things.
First, you need an account on FM.net (ForzaMotorsport.net)
Second, you will need an account on an image hosting site. There are quite a few. Imageshack, Tinypics, Photobucket and Flickr are some of the more commonly used ones.
Now for the fun stuff. Upload your saved picture in the game to your storefront. Then log on to your account on FM.net. On the My Forza page you will find all the pictures in your storefront with the option to download. Download the pics to your computer.
At this point you can edit them using a photo editor such as Photoshop if you wish. It's usually a good idea to at least change the size so they fit on the forum nicely.
Finally, upload the pictures to your hosting site. All the links to share them are usually provided by the site. You want the one for forum embedding for posting here. Copy that link, then paste it here on the forum.
Sounds like a lot, but it's not that bad.
If you run into trouble, don't be afraid to ask. We have a whole bunch of very computer savvy members who will gladly help you out. Took me a few tries to get it right!