Story highlights Bob Levinson was last seen on Iran's Kish Island in March 2007 during business trip, family says

The photographs show him shackled, wearing a jumpsuit and holding signs

"I feel Iran needs to resolve this now. It's been six years," his wife tells CNN

In the photographs, retired FBI agent Bob Levinson stares straight at the camera and holds signs, his hands shackled.

Reflecting a poor grasp of English, one note reads: "WHY YOU CAN NOT HELP ME." Another states: "4th YEAR ... You Cant or you Dont want ...?"

On Tuesday, Levinson's family released the images, showing the former agent in an orange jumpsuit with long, unkempt hair. A family spokesman told CNN the photographs were received in April 2011.

Asked why the family is releasing the images now, more than 18 months later, the spokesman said: "The family is anxious that not enough is being done. There is frustration with the lack of progress on the case."

"We hope it will get things moving," the spokesman said.

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Levinson was last seen on Iran's Kish Island in March 2007. According to his family, Levinson was working as a private investigator looking into cigarette smuggling and disappeared during a business trip there.

The family and the U.S. State Department have repeatedly denied he was working for the government and have urged Tehran to find him.

"I feel Iran needs to resolve this now. It's been six years," Christine Levinson, the missing man's wife, told CNN.

She said her husband will likely miss another family milestone this year; their daughter is getting married in February.

"He looks healthy, but I'm concerned about his health. I understand that he's being seen by a doctor three times a week and, if true, that's not good," she said, describing the photographs as disturbing.

Levinson suffers from diabetes and appears to have lost 50 to 60 pounds since his capture.

U.S. officials believe Levinson, now 64, is being held hostage somewhere in southwest Asia. While it's unclear who is holding him, a source with knowledge of the case said based on the evidence, there is every reason to believe that Levinson is alive and well.

In 2010, Levinson's captors sent a "proof of life" videotape and photographs of him to his family. Those images were released to the public in 2011.

The FBI has offered a $1 million reward for information leading to Levinson's safe return.