Unlike raster images, vector images are made up of shapes, not pixels. Vector images are drawn, usually with Adobe Illustrator. Raster images are created with digital cameras, and are modified and manipulated using Adobe Photoshop. There are advantages and disadvantages to using either type of image. If you are new to using vector images, there are many reasons to use vector images, but it's important to know when to use them.
Vector images are not photos, they are drawings. And that means anything from technical drawings, to logos, to animation. Since they are created with shapes, not pixels, they are never going to look exactly like a photo.
• Use a vector image when you need to reproduce an image on a t-shirt, or embroidered on a hat, or do a stencil.
• Use a vector image if you need to enlarge for a billboard, a large sign, or the side of a truck. A vector image can be enlarged without any loss of sharpness.
• Use a vector image if you don't want to worry at all about resolution. If figuring out pixels per inch at 100% makes you a little crazy, use a vector image, you don't have to think of resolution or pixels, because vector images don't have anything to do with resolution, or pixels.
Vectors won't work for everything. If you need a photo, you must use a raster image and you must use Photoshop. But if you can use a vector image and you have the original vector art, like this American Alligator in 16 vector colors, which you can find here, you can do a lot of cool things with it!