There are a number of free image sites available online. Many are a combination of free and premium, so make sure you are limiting your search to what you want. Additionally, the IT Web Services has posted some web-optimized images on the CMS Demo site.
It is important to resize images before you upload them into the CMS. This simple task will help you optimize page loading times and the user experience on your site. Uploading images directly from the source, such as a digital camera, and resizing the image via html or the image editor can significantly increase load times, especially if you have several images on one page.
Most CMS templates have a usable width of 900 pixels.
See Updating an Image for more image options.
You can't upload files that have special characters such as * or ( ) in the file name. If you get an error, rename the file on your computer to all lower case, with dashes instead of spaces, and then upload it again.
There is a file size limit of 15MB for uploads into the CMS. If your file is larger than 15MB, try optimizing it or using a lower resolution to reduce the file size.