For publication, you want to aim for high-resolution (more detailed) images.
Resolution can be measured by the number of pixels in the width x the number of pixels in the height of an image and also by the density of pixels per square inch, and the higher the numbers the better. Ideally, you want to use an image that is 250 pixels per inch (ppi) or greater.
An easy formula to use, courtesy of Colgate University’s Visual Resources Library, is the following: pixel dimensions ÷ 250 = largest size (in inches) you can print successfully.
For example, for an image sized 1024 x 768 pixels with 250 ppi, the largest you would want that image to be on the printed page is about 4 inches x 3 inches.
Let’s say you are printing a poster that is 11 x 17 inches. For an image to look good you will want it be at least 2750 x 4250 pixels at 250 ppi or greater.
x/250 = 11; x/250 = 17