The photograph of him used to make the wanted poster originally appeared on posters for his 2004 general-election campaign.
"It's almost like out of a comedy if it didn't deal with matters as serious as bin Laden and citizens' security."
Llamazares planned to ask the US government for an explanation and said he reserved the right to take legal action.
Llamazares said he was concerned to see the government resorting to what he called sloppy techniques, especially in the light of recent terrorism alerts such as the attempted Christmas Day bombing of a Detroit-bound airplane.
"It might provoke mirth, but it demonstrates that what we're seeing from security services isn't exactly recommendable," he said.
The wanted poster appears on the State Department website rewardsforjustice.net, listing a reward of up to $25 million. The FBI said the photo of bin Laden would be removed from the Web site.
Ken Hoffman, an FBI spokesman, acknowledged to the Spanish newspaper El Mundo that the agency used a picture of Llamazares taken from Google Images.
In a statement on Saturday, the agency would say only that it was aware of similarities between their age-progressed image "and that of an existing photograph of a Spanish public official."
"The forensic artist was unable to find suitable features among the reference photographs and obtained those features, in part, from a photograph he found on the Internet," the FBI said in a statement to the Associated Press news agency.
Bin Laden, who is wanted in the September 11, 2001 attacks and the 1998 US embassy bombings in Tanzania and Kenya, is believed to be hiding in the lawless Pakistan frontier bordering Afghanistan.