I've mentioned before that one of my hobbies is photography. Living in the North, there's plenty of ice and snow available from November to March, and here are two (out of many) pictures of ice I've taken in the depth of winter:
They struck me as having a slightly alien quality. So what to do? Given that I used a dSLR at 18 megapixels, cropping is an option, particularly since Kindle caps the image size of an e-book cover. Here's an enlarged snippet of the photo on the left:
It looked like an offworld apartment house to me. First I used Sketchbook's airbrush tool to tune it up, then added the other photo, the swirly one, to make the scene a little more alien.
Many programs for stacking photos are out there, such as GIMP and PhotoShop, but for fun I used Autodesk's SketchBook Pro app on an iPad 3, which at high resolution (1800x2400) offers up to four layers. Using Sketchbook I pasted the swirly image into a blank layer, flipped it horizontally, then slid it behind the apartment house.
On the Sketchbook layer menu, there are four options that determine how the stacked imagery shines through. I used the "Add" option in Sketchbook's layer menu, and the "set transparency" slider control to lighten up the interstellar cloud a bit.
The final step was to export the image via DropBox to OpenOffice's presentation module to add some lettering, and voila, a cover mockup:
"PHA"? It's NASA-speak for Potentially Hazardous Asteroid. Here's a link to PHA info from NASA, via Google cache, which has been quite handy in these days of government shutdown.