The rallies to mark the anniversary of the 1979 revolution are an uncomfortable mix of festive gaiety and political posturing. Walking down "Revolution Street" towards "Freedom Square" there were people begging to have their photos taken. Every time I stopped to point my camera, passing groups would shout for me to look. Kids in camouflage gear and pro-Palestinian check scarves puffed out their chests and waved their flags more vigorously. At one point a group of about twenty-five men all lined up neatly and patiently for me. Best of all, one middle-aged lady sitting by the side of the road looked up at me as I passed – her eyes just begging me to take her picture. She smiled a sweet smile, beaming innocently and incongruously over a poster showing the frankly lascivious grin of Ayatollah Khamenei and a black and white "death to America" placard.

So, in fact, Iran's biggest show of nationalist pride is actually one of the easiest times and places to take people's photographs. With the whole day almost entirely devoted to showing defiance against foreign meddling, the theory is, the further this message travels the better. And since "the enemy" speaks English, it makes sense to translate the printed material for their benefit as my friend Roland Platteau has oberved.

The national psyche has been so long moulded by opposition and Iran's pariah status in the western world that I even sensed a degree of knowing self-parody. Chanting slogans against America, Israel and, to a lesser extent, Britain has taken on the air of a national pastime. The role of 22 Bahman (11 February) as a political as a national day of rememberance has at least been equalled by its new role as a street festival – a kind of super-politicized Carnaval. There was even a tent by the side of the road giving kids the opportunity to throw darts at a crude mockup of Uncle Sam. A geopolitical fairground game. The host was wearing a comically-tall stars and stripes top hat.

At any other time, taking picture in Iran can be sensitive to say the least. And it’s hard to put your finger on why. Once I was taking a picture of bus. A normal city commuter bus. A plain clothed man, no uniform, no ID approached me and asked me if I had permission to take pictures. I said that we were in a public place and there was no need for permission. He assured me that I was wrong. After some time talking I think I got to the bottom of it. He told me that many foreigners come to Iran and take pictures of things to present Iran in an unfavourable light. I asked him what about the good things in Iran? What if foreigners want to show Iran in a good light? I had taken my picture and he was getting bored so we parted without reaching a conclusion.