It's a black & white bare picture you add where a normal picture goes. It's for people with slow computers. It shows the black and white one until the full colored pics load.
Given that search engines don't actually look at what the picture IS, in terms of SEO it would do exactly two things.... and Jack left town.
Yeah, don't use it. Besides, almost nobody has a "slow" computer anymore, and those with dialup (such as myself) will either wait patiently for the image to download (like I do) or disable images from being downloaded via their browser preferences (which is why presentational background images applied via CSS should have background colors stated as well).