The images used on the web have been compressed so that the web pages load quickly. As a result, much of the detail has been lost. In fact, web images default to only 72 dpi. I am often faced with the challenge explaining to clients why web images won’t work for their print projects.
I illustrate it this way: If you squeeze all of the toothpaste out of the tube and then try to put it back in again, what will it look like? Pretty bad. It is the same with web imagery. All of the details have been “squeezed out” and cannot be put in again. Thus they cannot be used in print work which requires 300 dpi images to be successful. Remember this the next time you want to snatch a web image for your print job. Be sure to use vector-based, scalable imagery or high resolution photography to insure professional results.