How do I get different background images on my dual monitors?

The answers so far are good, but I thought there must be an open source tool that does this.

It turns out there is: Dual Monitor Tools

This is a set of Free (open source) utilities. It can configure wallpaper for a dual-screen setup. It can mix both landscape and portrait-mode monitors.

It also has several other tools, including a screenshot utility.

I can run one desktop background image spanned across both screens out of the box, with no extra software installed. The trick is to find an image that matches the resolution of both screens together. In my case, with 17" monitors both at 1280x1024, I need an image that is 2560x1024.

Now go to Control Panel>Apperance and Personalization>Personalization>Desktop Background and select the image. Then set the picture position to "Tile". Your background image should now be spanned across both screens.

As far as I know, this is the only way to avoid having the same image on both screens without installing 3rd party software. There is not a way to have a different image for each monitor unless you save two images next to each other as one file with the correct resolution for your monitors, giving the appearance of two separate images once applied.

If you're looking for a good source for images that match your screen resolution requirements, interfacelift.com is a good source. You can browse by resolution size and they have a wide variety to fit a range of different tastes.

Not out of the box, but Display Fusion works perfectly (free version is good enough)

You can either set up different wallpapers on different screens or span one wallpaper over dual screen.

Works great with my dual 1920 x 1080 setup.