Microsoft's terminology in PowerPoint can be confusing. There are two major types of "graphics" you can add to a slide, both referred to by Microsoft as "pictures." One type of picture is a photograph; another is an illustration which may or may not look particularly realistic. This second type of graphic, the illustration, is referred to by many graphic designers as clip art.
Photographs are stored in a "bitmap" format, that describes each dot of color in a picture. This allows for significant detail and color variation, but results in a larger file that does not scale well. If you have ever enlarged a picture, you know it can become pixilated. And if you reduce a picture too much, detail in the picture (even a person's eyes) can disappear.
Illustrations (clip art) are generally stored in a "vector" format that describes the picture mathematically. Typically, clip art has far fewer colors and less detail than a photograph, but the file size is significantly smaller and the image can be enlarged or reduced in size with no loss in quality.
Microsoft Office uses the term "clip art" in several contexts. First, in the context of the Clip Art task pane, clip art refers to media that is stored in the Clip Organizer, indexed categorized for easy search. The Clip Organizer, and the Clip Art task pane, manage pictures, illustrations, videos and sounds.
However, when you use the Clip Art task pane and search for media using Clip Art as your choice in the Results should be list, Clip Art now refers only to illustrations.
The major differences between clip art (illustrations) and photographs are summarized below:
- Photos can support more color and detail
- Clip art can "size" more effectively, enlarging or reducing without loss of detail.
- Many photos can support transparency. Clip art is only transparent where there is no background and no fill color.
- Clip art can be recolored within PowerPoint. You would need a photo editor to retouch a photograph.
- Clip art is much more efficient from a file size perspective than photos, though at least PowerPoint now supports compressing photos.