Image download files can be purchased in four sizes:
Web (640x480 up to 0.3 Mpix),
Low-Res (1 Mpix)
Hi-Res (4 Mpix)
Original (varies)
Original image sizes range from approximately 4800 to 10800 pixels on the long side of the image at a resolution of 300 ppi. They are considerably larger than the preview images you see on the site. The example below shows the difference between a detail section of the largest watermarked Preview image (right) and the full size Original image available for purchase (left).