Caterina Fake and Stewart Butterfield, founders of Yahoo's photo sharing subsidiary Flickr, have left Yahoo, according to the Web site TechCrunch. Fake officially departed last Friday, and Butterfield (her husband) is expected to leave July 12.

The ValleyWag Web site reprinted what it said it a copy of Butterfield's resignation letter to his boss, Brad Garlinghouse, senior vice president for communications and communities. In the letter, Butterfield joked about his tenure at the company, but was dead serious in explaining his reasons for leaving.

"I don't know what you and the other executives have planned for this company, but I know that my ability to contribute has dwindled to near-nothing, and not entirely because of my advancing aging," wrote Butterfield. "Therefore, with a heavy heart, I recognize that it is time for me and the company to part ways."

Yahoo bought Flickr in March 2005 for a reported $35 million. In December that year, Yahoo furthered its Web 2.0 properties with the acquisition of bookmarking service del.icio.us.

The resignation of the Flickr founders comes on the heels of yesterday's announcement that Jeff Weiner, executive vice president of the company's Network Division, is leaving to work with venture capital firms Accel Partners and Greylock Partners.

In recent weeks, Yahoo has seen the exit of Jeremy Zawodny, a technology evangelist, and Dr. Usama Fayyad, executive vice president of research and strategic data solutions.

Other Yahoo employees that have departed earlier in the year include Bradley Horowitz, head of Yahoo's advanced technology division; Salim Ismail, head of Yahoo Brickhouse; Jeff Bonforte, vice president of social search; Ian Rogers, vice president of Yahoo Music; and Matthew Berardo, senior director of International Business and Product Management, according Tech Crunch.