We offer all our pictures in one download size, 2880x1800 (which will open in a new window when you click the picture or text link on one of our preview pages). Our 2880x1800 backgrounds will look good (and sharp) on any display using a "stretch" control panel setting, which you'll find on almost all Mac and Windows systems. If your control panel is already set to a "stretch" option, our pictures will fit your desktop without any cropping, but...
For these 16:9 HD formats, "stretch" options will look good, but you could also choose "Fill" (Windows 7) or "Fill screen" (Mac OS X), which will crop a little off the top and bottom of our pictures to fit your widescreen display, instead of "squeezing" them vertically. You could also try "Fit" (Windows 7) or "Fit to Screen" (Mac OS X), which will display images as large as possible on your monitor without cropping or stretching, but will leave empty space (on the sides, for this format) that you can fill with a color of your choice.
These 16:10 formats match the proportions of our backgrounds exactly, so "Stretch" on Windows 7 and "Stretch to fill screen" on Mac OS X will resize our images to fit your display without changing the proportions, and without any cropping or loss of quality. (Actually, "stretch," "fill" and "fit" will all do exactly the same thing, since the proportions match.)
On 4:3 monitors, we would usually choose a "stretch" option, which will "squeeze" our images horizontally (and in most cases will be close to the original camera format). If another setting would look better, we'll add a note in the description of the preview page.
For 5:4 displays (a fairly square format), you could try a "fill" option (which will crop off the sides of our pictures to fit this format), or a "fit" option (which will leave empty space at the top and bottom of your display). For most photos, especially abstract and scenic nature wallpaper, we prefer to fill the screen using a "stretch" option to keep everything in the original composition. For desktop backgrounds featuring symmetrical subjects, though, like people (or flowers), "fill" or "fit" settings will keep the proportions of the image you download.
3:2 displays are proportionally almost the same as 16:10, so "stretch" will keep the shape almost the same as our original background pictures, while "fill" will crop a little off the sides.
Bigger than 2880x1800...
There aren't many monitors with a resolution higher than 2880x1800 (which is the size of Apple's MacBook Pro Retina display), and when there are, we'll update the size we offer. Whenever the background image you want to use is significantly smaller than your screen resolution, choosing a "center" option will avoid any loss of sharpness.
As long as you leave our logo and copyright notice on the picture, provide a photo credit linked to Desktop-Backgrounds.com on your site (which happens automatically when you pin to Pinterest, for example, or paste the address of a page into Facebook), and aren't making our images available for sale, printing or download (as wallpaper or print resolution files, for example), our pictures are free for your personal use. And, of course, our high-resolution desktop backgrounds are always free to use as wallpaper on your personal computer. If you would like to use our pictures commercially, please contact us for licensing information — we offer higher resolution images without logos or copyright notices for stock photo use.
To change your control panel settings...
On Windows 7, right-click any empty area of your screen, choose Personalize, then click Desktop Background and choose one of the positioning options.
On a recent version of Mac OS X, control-click any empty area of your screen, choose Change Desktop Background..., then choose a positioning option.