The image files you have been working with so far in this section are all bitmap images. This means that they contain pixels. Each pixel is a tiny little dot of a certain color and it is the collection of all these tiny little colored dots that recreates the picture as you see it.
Bitmap images are great, but they have one important limitation. To guarantee the best possible image quality, you must consider that a bitmap image is designed for a specific size. You should use an external application (such as Adobe Photoshop) to generate the image. You should not resize the image after you insert it in Captivate.