How can I see the size in pixels of the photos I am using?

The size of your photo determines the size of the picture you can print. A "pixel" is a picture element, which is also called a "dot." 300 dots per inch will make a near-perfect photo, so an 8x10 that is 2400x3000 dots is an excellent photo. 180 dots per inch is acceptable for most printing, but we recommend against lower dots-per-inch (dpi) except on very large posters.

To examine the size of your photos, enter an album, choose Organize, and then Edit Titles:

The Width and the Height of each image in the album is displayed in pixels. For example, the first image is 4800x3229 dots: