How would you feel if a complete stranger had a photograph of you on their fridge? Your hair a mess at the end of a tiring day, caught at an unflattering angle in your oldest clothes, damp and sweaty, longing for a shower.

You might feel that your soul had been stolen – plenty of people see cameras as frightening, not just annoying – or you might just be furious that your privacy had been violated by someone who doesn’t even know your name. A few years ago a group of young Chinese men surrounded me at a tourist spot in northern India, friendly, laughing, snapping away. I asked them to stop, but they didn’t. A tiny window into the lives of those whose faces pop up as screen savers the world over.

It can be tempting just to snap away vaguely, presuming it does no harm, but a quick walk round the block in someone else’s shoes provides a sharp reminder that it does. Many people who go on slum or township tours equate the experience to a trip to the zoo.

Enough.

Clicking the shutter should be the last thing you do.

Why are you taking the picture anyway? What will you use it for?

Now we don’t have to load film, check it’s caught, wind on, keep it in a dark place, make sure it’s developed safely and hope, pray we got the shot we saw. We’re digital, we’re point and shoot, we can take thousands of frames at no extra cost.

Yet it’s no coincidence that most photographers who have worked for long periods in war zones, disaster zones and among the desperately poor, are haunted. One ex-Sunday Times reporter told me he could not longer take those pictures after his first child was born.

You want to show people what you saw, but don’t give up on words. I won’t forget watching a student tell a friend about her day at a school in a South African township. Her voice became soft and tears came to her eyes as she realised that the children she was describing were far too small for their age because they had never had enough to eat. Talking forces us to engage; photography can let us off the hook.

Use the power of your camera wisely. Access to the lives of others is a privilege, so bring both good intentions and a critical mind.

Don’t forget to capture details, insights on the condition of people’s lives. Look for the things you can’t see. A near-empty drugs cupboard in a hospital can tell you far more than a picture of someone dying, and doesn’t compromise anyone’s dignity. Heads bent over a shared textbook, an unnecessary flower garden, feet in new shoes.

Seek out contrasts, juxtapositions that illuminate. Ordinary objects that tell stories.

Talk to people. Introduce yourself. Ask.

Sometimes people say no. Perhaps one of their friends, or someone nearby will say yes. Take the photo. Show them. Do it carefully, move to catch the light and their best angle. Many people have never seen a photograph of themselves. Don’t start if you don’t have time to finish.

Last January I was in Tamale, northern Ghana. I walked through the market with a local guide. He knew everyone, they catcalled as we went past. With his permission I took shots of the market, a riot of colour and activity. But I wanted the women. So I asked. Some said no. Some said yes. I started taking pictures and when I had a good one, I showed them. They were delighted. They were beautiful, astonishingly beautiful. Those who had said no, now fought to be next in line. We laughed, I teased them, they teased me, we had fun.

I took their names and asked permission to use the photos. Although I had showed everyone their pictures, I couldn’t give them copies. I promised I would send them, and I did. I don’t know if they arrived. If I could have done I would have printed them on the spot. We lost something very precious with the demise of the polaroid. I was converted after a trip to a remote part of Madagascar in the mid 90s by friends who insisted on taking and giving people their photographs. I had been completely against the idea. I could not have been more wrong. What could be more precious than a picture of your family?

Don’t underestimate the power of photography. In thoughtful hands a camera shrinks space, connects strangers and illuminates lives. In thoughtless hands it snatches and grabs, hits and runs, confirms stereotypes. Used to tell stories it is still the magic lantern that captivated our forefathers and made us leave home in the first place.

* See Susan Sontag’s 1977 book of the same name, and her later Regarding the Pain of Others. Also The Bang Bang Club and Ken Light’s Witness in our Time