What Is The Best Resolution For Posters and Banners?

Please use image resolution of 200 dpi at full size as much as possible.  No lower than 150 dpi and no more than 300 dpi. That means if you have an image that is, for example, 8" x 10" at 300 dpi, it can be blown up 300% to 24" x 30" to give you a final image of 100 dpi. Often it is difficult to find images of sufficiently high resolution and customers will "cheat" by "sampling up" a lower res image. There is no point in doing this. If all you have is an image with an effective resolution of 50 dpi at full size, then sampling it up (to, say 100 dpi at full size) will not give you more detail. It will just give you a much larger file with the same amount of detail.

For banners or posters - it is better to provide vector artwork from programs like Illustrator because these are line art and will produce the sharpest result and also will have small file size.