From BlenderWiki

[edit] Stamp Panel

The Stamp panel is used to overlay some information on the rendered png or jpg image so you can see where and when an image came from. This is essential when using Blender in teams or where there are review cycles that give critique and feedback. The process is in two steps:

1. Set up the Enable Stamp settings
2. then when you are ready to stamp, enable Draw Stamp

The desired information is overlaid in various corners of the image.

[edit] Enable Stamp

Set this up once for the standards used in your shop, to select what to display.

Filename

full pathspec and filename UR corner top line

Scene

Scene name within the .blend file

Camera

Camera name within the scene that took the shot. Bottom Center

Time

Duration into the video, in H:M:S.ss. LL corner

Date

Date frame was rendered MM/DD/YY format. UL below Note.

Frame

Frame number. Useful for key stills. LL corner after Time

Marker

Displays "Marker" as second line up above Time, and <none> until a marker is passed in an animation.

Sequence Strip

If Do Sequence is enabled, the name of the strip. UR corner.

Note

Enter any comments into the text field. Overlaid as UL corner below Filename

[edit] Draw Stamp

When enabled causes the Enabled info to be overlaid

Font

Some easy choices of fonts to use

Text Color and Background

Click the swatches to change the font color and background

A - alpha

Sets how transparent the text is