Britney's Gleeking out!

On Wednesday, Britney Spears sent her first Tweets -- and a photo! -- from the set of Glee, where she's begun filming her scenes for the upcoming "all-Britney" episode.

"About to do my first shot of the day for Glee tweeties! Here we goooo!" the pop star, 28, wrote. A few hours later, she added, "what's up GLEEKS? Having so much fun on set!! Can't wait for you guys to see the episode!"

In an accompanying TwitPic, Spears seems to be in costume: wearing clear plastic-framed glasses and a gray top that, perhaps, a teacher might wear. (She stands next to her assistant, Brett Miller.)

Glee creator Ryan Murphy was vague on details about Spears' special episode during a radio appearance last week. He teased that Spears may show up when members of the show's glee club hallucinate while under anesthesia at the dentist. "They have fantasies of how they can be like her," he explained.

Murphy added that the episode is "so reverential about her...It's about her music and it's not about her personal life."

Spears also used Twitter last week to announce her return to the recording studio, where she's begun work on the followup to her 2008 smash comeback Circus.