The number of megapixels (MP) required to produce photographic images and prints of various sizes is something with can be debated endlessly. However, images in magazines and books are generally printed at a resolution of 300 dpi so this can be used as the basis for a general guide. Prints of a reasonable quality can be printed at resolutions lower than 300 dpi but the acceptability of the print will depend not only on the perception of the viewer but also on the subject of the image. A picture of a misty landscape is likely to be much more tolerant of low resolution than a close-up portrait or a wildlife image.
The following table provides a general guide to the number of megapixels required to produce magazine-quality resolution.