The resolution of a digital image, expressed in pixels per inch (ppi), is an expression of how much detail an image holds. Higher resolution means an image has more detail and therefore appears crisper. For printing of documents, we recommend a resolution of 300ppi for images at the size they are actually printed (although a resolution of 200ppi or greater will generally produce acceptable results). For large format printing, such as large banners and trade show backdrops that will be viewed at a distance, we recommend a resolution of 100ppi for images.
You can use software such as Adobe Photoshop to change an image's resolution, or you can simply print the image at a smaller size to effectively increase its resolution. For example, if you have an 8"x10" image at 150ppi, you may see some pixelation if you were to print the image at this size. However, this image contains the same amount of detail as a 4"x5" image at 300ppi (doubling the resolution effectively halves the image dimensions). At this size, the image will look much clearer and crisper.