Comet C/2011 L4 PanSTARRS captured in the blow resolution beacon images for the STEREO Behinds H1 imager. With the comet only 0.8 AU from the STEREO imagers, and around magnitude 0 from the spacecraft, the comet and its tail is over exposed on the low resolution beacon images, making it look like a bright come at the bottom of the image.
In a few days I will be able to download the high resolution images, but it is likley to be over exposed on them too, as the CCD camera is designed to pick up the dim coraolal mass ejections and solar atmosphere.
Also in the image is Mercury (up close to the Sun) and Earth (the bright dot centre right).
Here's an animated GIF.