Our least favorite phone call to make is to let the customer know that we cannot print their files as submitted because some graphics were downloaded from the web.
The reality is, web graphics and screenshots are pretty lousy quality. They don’t contain anything like the amount of information you’ll find in a print graphic.
The result is that your image will not be brilliant, and you will probably be able to see more pixilation than you thought there would be when you viewed it on your screen.
Printing is not done in continuous color, the ink is laid down on the sheet of paper in dots of Cyan, Magenta, Yellow and Black (CMYK), lots of tiny little dots giving the impression of continuous color. These are the dots referred to in the term DPI (Dots Per Inch), while in web terms these are referred to as PPI (Pixels Per Inch). In almost all instances these translate 1 to 1 (DPI to PPI).
The common PPI for web graphics is 72ppi and they look terrific on your screen, but herein lies the problem when they are converted to print. The precision of ink on paper is so that unless you are printing at 300dpi the image will look like an old school comic strip where you see all of the dots.
4 Tips to make your web graphics look better when printed:
Reduce the size of the graphics to be 1/3 or 1/4 of the original size. Reducing the size increases the dpi resolution. Half the size doubles the resolution (72ppi becomes 144dpi) which is still rough but better, and one quarter of the original size multiplies the dpi four times (72ppi becomes 288dpi) and that is good enough to print.
Print out & Scan your graphic at a higher resolution is a good quick fix that you can do yourself and will make your graphic appear a little better than a web file.
Get the original file from the designer who created it. This is the best solution because may be as simple as saving the raw file in a different format.
Redraw the image. A designer can redraw the image from your low-resolution web graphics and save it as a printable graphic. This option is not as expensive as you may think, but it depends on the detail in the graphic.
Options 3 and 4 above will give you the best quality reproduction of your graphics when printed on paper or any other substrate, and the investment is a one-time cost that will improve the quality of your printed material for current and future projects.