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Jpeg and Gif files are Internet images, saved with a compression process designed to remove color and visual quality to achieve small file sizes. Internet images are usually saved at a resolution of 72 dpi for quick screen loads and will not print clear and crisp on a printing press.
Since the physical dimensions of an image and resolution are in direct proportion to each other, shrinking the physical dimensions of an Internet image by 4x will achieve decent printing results (72dpi x 4 = 288dpi). Here's how to calculate the size you must reduce (shrink) an Internet image to get it to print well: reduce the size to 24% of its original size (because 72dpi is 24% of the 300dpi resolution you want). For example, if an Internet image is 3 inches x 3 inches, at 72dpi you want to shrink it enough to get it to 300dpi for crisp printing
Zoom into your images to see the quality. Be aware of your design, purpose of your printing, and the needs of your customers before using images from the Internet.