Updated: 2/26/11: Cover is "War of Green Lanterns" related.
The DC Blog The Source posted an interview with "Flashpoint" artist Andy Kubert and also posted this cover to a Green Lantern "War of the Green Lanterns" issue.
This appears to be from Clayton Crain as the artist tweeted:
"Finished three Green Lantern Variant Covers for DC Comics."
Highlights from the Andy Kubert interview include how he became involved with "Flashpoint," working with Geoff Johns, his favorite character to draw, the biggest challenge working on a project such as this and on keeping the secret about "Flashpoint" for so long, Kubert said:
As a lot of people know, I teach and work at my father’s art school where I have an office and studio. Everytime I go into class or walk down the halls, I get peppered with questions from students about Flashpoint! I just look at them and laugh and either say I can’t answer or just make something up to get a reaction. Then say I was only kidding! It’s been a lot of fun! Usually I tell them to go read the Sources’ Flashpoint Fridays cause they’re not going to get anything out of me!