Compatibility

Choose a graphics application that can generate JPEG or GIF Images for display in your web browser.

Image Size

Unless you are creating a background image, the recommended size range for graphics are from half to quarter of the available window space on your page.

So if you are using 800 x 600, and you have equal text and graphics, the graphics image space available would be 400 x 300.

Less text means more graphics space or white space is available.

Image Resolution

It's okay to generate Images with higher than 72 pixel/inch resolution, however keep in mind that the larger the file size, the longer it takes to display on the web page.

The general practice is to create Images with 72 pixel resolution in either JPEG or GIF format.

Copyright

Be aware of copyright implications when you are creating your website graphics. If your Images are available to the public, they can be downloaded or copied with little difficulty.

This applies to your logo, product photos, anything that you display on your website.

Similarly, if you want to use someone else's graphics, you must ask them first. Companies can often use each other's graphics if appropriate terms are negotiated and credit is displayed on the website.