Yahoo founder Jerry Yang is stepping down as CEO, and a search is underway for a replacement after a tumultuous 18 months on the job. Which is curious. In a recent interview, Yang had just told AllThingsD's Kara Swisher, "In this uncertain environment, I think I am absolutely the right person" to lead Yahoo. He must have changed his mind; Swisher reports that the decision was a "mutual" one made by Yang and Yahoo's board of directors. Either Yang was lying to Swisher, or he was deceived about the board's lack of support for him. Executive recruiter Heidrick & Struggles is conducting a search for Yang's replacement. Finding a successor to Yang will be difficult — not because Yang is irreplaceable, but because he has made such a mess of things that it will be hard to persuade a capable executive to risk their reputation fixing it.There are, nevertheless, some possibilities. One is former eBay CEO Meg Whitman, who has been toying with entering politics. eBay and Yahoo have long flirted with a merger, so she's reasonably familiar with the company, and with the challenges of running a large Internet company. A similar candidate: Jon Miller, the former CEO of AOL, who is now a partner at Velocity Interactive Group, a venture-capital firm. Money is tight in venture capital, and Velocity has yet to raise a promised new fund in the multiple hundreds of millions of dollars it had planned for when he joined it. Yet Miller has a problem: Time Warner, the parent of AOL, used his noncompete agreement to prevent him from joining Yahoo's board; it's not clear why they would waive it to let him become CEO. The agreement does not expire until next spring. News Corp. COO Peter Chernin does not seem to have much hope of succeeding Rupert Murdoch as CEO, who is expected to hand the media conglomerate over to one of his children instead. But he does not have a credible claim for having much online experience — overseeing MySpace is the best he can do there. And lastly, as a courtesy, Yahoo's president, Sue Decker, is under consideration. Some say Decker's Machiavellian maneuverings helped out former Hollywood studio boss Terry Semel as CEO last summer. But she's seen inside and outside the company as a bad manager who lacks a vision for what Yahoo should be. More: