Using Digital Images
This guide outlines practical teaching and technical points you may find helpful as you plan to work with digital images.
Images add color and visual interest to Web pages and PowerPoint presentations. They can help break up plain text, communicate information pictorially, and unify the look and feel over a series of Web pages or slides. However, using too many images or graphics which are unrelated to the topic may be distracting.
Use images in your teaching.
Images can take a variety of forms and serve numerous purposes in the context of your course. Research suggests that for certain kinds of tasks, images combined with text is the most effective means of information transfer. Placing images such as charts and graphs, concept maps, flow charts, and photos on your Web site also makes them more accessible to your students. Be aware that images can compete with text for your students' attention, so be selective and choose images which will add to student learning. Including graphics unrelated to the text can be confusing.
Obtain images from a database
The UW Libraries Image Collections contain databases of graphics on everything from ballroom dance instruction manuals to "American Indians of the Pacific Northwest". Each database has different usage policies, however, most of them allow you to share the images with UW faculty, staff, and students. Some of the more popular collections include "Corbis Images for Education", Associated Press ("AccuNet/AP"...) archive, and the Camio catalog of art museum images.
Determine appropriate file format.
Most images used on the Web will be either .JPG or .GIF format. Generally, images that use a very high number of colors, such as photographic images, should be saved in .JPG format. Web images with limited colors, such as icons or clip art, will usually be in .GIF format. PowerPoint can import images saved in both of these formats, as well as .PCT format for the Macintosh and .BMP format for Windows-based computers.
Economize file size with image resolution.
Computer monitors are generally limited to a resolution of 72 dots per inch (dpi). If you are using images in a PowerPoint presentation or as part of a Web page, image resolutions higher than 72 dpi are probably wasted file size and result in slower download times. Many photo-editing programs will automatically save your images at a lower resolution when you specify that you want to use them on the Web. For example, in Photoshop, select File > Save for Web. Printers, on the other hand, can commonly reproduce images of 600 dpi resolutions or higher, so you might consider a higher resolution for images you wish to print or use as archival copies.
Adjust physical size.
As with resolution, the physical size of images contributes to the amount of disk space the image will require. For Web pages, keep images as small as you can without sacrificing quality. This will afford your viewers much quicker access to your Web pages, and will keep them from having to scroll down the page to view the entire image. Images should be no larger than 550 pixels wide by 375 pixels high (about 3" x 5"), though it is best to make them considerably smaller than this if possible. Using lots of large images in PowerPoint screen presentations can also cause your computer to balk if it is an older machine. Be sure to do a trial run before your presentation. Read our documentation on changing the image size in Photoshop.
Consider copyright issues.
Images posted on the Web are covered by United States copyright laws in similar ways to material found in books, newspapers, and magazines. To learn more, see our Copyright Resources page.
Consider your use of colors
Don't rely on exclusively on colors to make points because not everyone can distinguish colors; colors may look different on different computers; and if you want students to print the images, colors with a similar brightness will look the same on a black and white printer. You may need to add text to explain your graphics.