A Charleston firm that built a photo-sharing business around the microblogging service Twitter said it's folding after Twitter threatened to shut out the local company over a trademark dispute.

Twitpic's technology was among the first to give users the ability to easily upload and link images and videos to their Twitter messages, or "tweets."

The East Bay Street firm plans to close Sept. 25 "out of principle," founder Noah Everett said in message Thursday night.

"This is an unexpected and hard announcement for us to make and we want to lay out what led us to this decision," Everett wrote in an earlier blog post.

He said Twitter contacted a legal representative for Twitpic a few weeks ago, "demanding that we abandon our trademark application or risk losing access" to the company's interface.

"This came as a shock to us since Twitpic has been around since early 2008, and our trademark application has been in ... since 2009," Everett said.

He added that his firm doesn't have the resources "to fend off a large company like Twitter to maintain our mark which we believe wholeheartedly is rightfully ours. Therefore, we have decided to shut down Twitpic."

Twitter created its own photo-sharing feature that began to directly compete with Twitpic about three years ago.

A spokeswoman for the San Francisco-based company responded to Everett's comments with a written statement.

"We're sad to see Twitpic is shutting down," Twitter said. "We encourage developers to build on top of the Twitter service, as Twitpic has done for years, and we made it clear that they could operate using the Twitpic name. Of course, we also have to protect our brand, and that includes trademarks tied to the brand."

Everett assured Twitpic users that they'll be able to export all photos and videos.

"We'll let everyone know when this feature is live in the next few days," he wrote.

Everett also thanked Twitpic users "for letting us be a part of your life and helping you share your experiences over the past six years, it's truly been an honor."

Last month, the 30-year-old Everett told The Post and Courier he was launching a new email service called Pingly.

"I'm still planning to go forward with Pingly and such," he said.

At pingly.com, Everett's messaging profile describes him as, "The nice guy that finished first - Founder of Pingly and Twitpic."

Andy Paras of The Post and Courier contributed to this report. Contact John McDermott at 937-5572.