High vs. Low Resolution
To determine whether your image is a suitable resolution for your specific project, you need to check its DPI (dots per inch). DPI is a measurement that specifically applies to raster (pixel) based images. Most commonly there are two sizes, 72 DPI (72 dots or pixels per inch) and 300 DPI (300 dots or pixels per inch). Raster images with 72 DPI are best used on the web while printed images should be at least 300 DPI. Resizing a low (72) DPI image pulled from the web to fit the higher (300) DPI requirement of your print project, is a common expectation. But attempting to resize an image in such a way enlarges the pixels, causing the image to become fuzzy and distorted. Often, so much that the pixels become large enough to see. The image becomes “pixelated” or blurry.
Vector vs. Raster
Raster images use pixels to form an image. Since raster images are constructed using a fixed number of pixels, they can’t be resized to create a larger image without causing the image to become distorted.
are constructed using mathematical formulas rather than pixels, therefore they have no ‘resolution’ and are excellent for creating graphics that frequently require resizing.