A vital part of web pages are the images that are used to illustrate examples or brighten up the page. However, there are several things to be aware of when you want to put an image on the web. By being aware of these things and modifying your images before uploading them you will be providing a better end user experience.
Key things to keep in mind are:
1. Images should be saved at 72DPI (Dots Per Inch). This the optimal DPI for displaying while keeping a low files size.
2. Images should be cropped to the size needed to fit into the space on the page. Once again, this will help reduce overall file size.
3. Images, once "saved for the web" should ideally be less than 75KB.
4. Text in images will not show up in search results.
5. For usability and search, all uploaded images should have a descriptive alt tag entered.