(CNN)It was 3:30 in the morning when Robert Alan Black was escorted into Khalifa jail. 

An American in Abu Dhabi, he found himself frightened even though the other prisoners were sleeping. Movie scenes from "Midnight Express" and "Brubaker" swirled through his head. 

He sat at a table in the common area, waiting for the others to wake, not knowing what the reaction would be to his presence. 

Black, who has a degree in architecture, three master's degrees and a doctorate in educational psychology, was in Abu Dhabi, the capital of United Arab Emirates, for October's Creative Thinkers Conference. He was to present a workshop and emcee the event. 

On a Tuesday morning, the 70-year-old got up early to take a walk in the neighborhoods near his hotel. An avid photographer, Black took his camera to snap photos of houses and a couple of the mosques he passed. 

When he left the second mosque, he was approached by a man in uniform. He motioned Black to get into a camouflaged truck. 

"I had no idea what he wanted," Black said, "but never felt threatened so I got in." 

He was driven a short distance to a building with a sign out front that read "Reception." He waited about an hour before he was guided back outside and told, "Do not photograph security areas." 

Black asked for clarification, but he was waved away with no further explanation, he said. 

He decided to continue his walk. A few blocks away, he came upon a sign on a lamppost that said in English, "Photography Forbidden." Thinking a photo of the sign would make for a novel Facebook post, he snapped an image. 
And for what conference?
 October's Creative Thinkers Conference