Peter Linsley of Google Images shares some simple yet important image optimization tips that might help you get more traffic from image search engines:

• Users prefer large, high-quality images (high-resolution, in-focus).
• Users are more likely to click on quality thumbnails in search results. Quality pictures (again, high-res and in-focus) often look better at thumbnail size.
• Distracting features such as loud watermarks, text over the image, and borders are likely to make the image look cluttered when reduced to thumbnail size.

Maile adds: Preview your images at thumbnail size to get an idea of how the user might perceive it.