Understanding Raster vs. Vector
There are two types of digital image files – vector and raster (or bitmap).
A raster image is made of a collection of dots called pixels. A 72 dpi image is made of 72 dots per inch (dpi) or 72 pixels (ppi) in every inch of that image. The number of pixels that comprise a raster image is called the resolution and it is fixed. If you take a 72 dpi image and scale it up 300%, you will not increase the number of pixels or dots of that image, you will simply increase the size of each pixel or dot. The result will be an image where you can clearly see the pixels and no fine detail - which is why we recommend you use a high dpi like 300 at size as to get a high-quality printed image. Photographs are raster graphics. Common raster file types include: JPG; GIF; PNG; TIF.