Designing for commercial printing requires higher-resolution images than those optimized for the web and video. The rule for offset printing is to double the line screen, meaning if your print vendor uses a 175-line screen, your photos need to be at least 350 pixels per inch (PPI).
Working smart: Whether designing for on-screen or print, you are better off creating original art in high-res and saving the source file separately before compressing a version for on-screen use. That way, if a client requests a print piece based on the artwork you have spent hours creating for their website, you'll have the high-res files ready to go.
Other print vs. online considerations: always create artwork in the RGB colorspace, and convert a version to CMYK for print. Also, understand when to use vector art (Illustrator), and when to use raster art (Photoshop/GIMP). For example, if you create a logo in Photoshop, it will not be crisp enough for print, and a good print house will request that it be reproduced as vector art.
Finally, if you are unsure about print specifications, don't hesitate to talk to your vendor early in the process.
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