Know the image size required for your layout before you purchase stock photography online. Read their information prior to purchase as it will determine, price, color, file size, copyrights, resolution and quality.
Each image should be at a resolution of 300dpi for the final size in your layout. Reminder: get the image in CMYK color mode (rather than RGB) if possible. Here are some guidelines for you to follow:
• 2 inches x 2 inches @ 300dpi = 600 pixels x 600 pixels = 1.38 MB
• 4 inches x 4 inches @ 300dpi = 1200 pixels x 1200 pixels = 5.5 MB
• 8.5 inches x 11 inches @ 300dpi = 2550 pixels x 3300 pixels = 32.2 MB