You may know about the vital public health services performed by the U.S. Centers for Disease Control and Prevention (CDC). But did you know that the CDC is also a fount of free images?

Media produced by federal employees in the line of their official duties are usually destined for the public domain. As a result, the agency's Public Health Image Library (PHIL) hosts a trove of images that can be used openly, without prior permission, for anything from science blogging to t-shirt design.

Below is a sampling from the CDC's electron microscopy files.

For more of the CDC's images, visit PHIL.