Generally, the smaller, less visually interesting, and more quiet a camera is, the more unobtrusive I have found it.
My most unobtrusive camera is the Ricoh GRD III. I went through a period of wearing it around my neck all the time, and almost never received comments or looks. Most people have no idea they are being photographed with it, although I have developed a casual style of shooting from the hip or the leg for street work. I haven't used the GR in this manner, but I imagine it would be more of the same. The GR series, with its rounded and unassuming lines and dulled matte finish, seems perfect for discreet shooting.
The only time the GRD III was noticed taking a photo was by a hotel assistant in Japan. I had it around my neck as my friend and I followed him to the hotel gym. The hallway wasn't silent, but fairly quiet, and the noises of lens extension, focus and shooting made him prick up his ears. He asked me not to take photos, something I found odd in a long and bare hallway. The GRD III's operating noises are the only thing that disappointed me about it, as the Canon S90 was faster to start, focus and shoot, and more quiet to boot. The extension noise of the III is a long wheezy mechanical creak, and the focusing and shutter sounds are still fairly audible. Especially to Japanese hotel assistants.
The Fuji X100 and X10 attract attention, ironically because they look like old cameras. 'What's that, is that an old camera? Does that shoot film?' You never get that question with a Ricoh GR/D. Same thing with the silver Panasonic GM1. That's received a few looks and comments, and someone asked if it was an old film camera. But I'd wager that a black GM1 with a pancake lens and electronic shutter would almost never be noticed.
Once you get past the very slow power-up time, the Sigma DP1 is surprisingly quiet.
Having said this, there is a difference between someone noticing a camera and noticing if you are taking their photo. Raising a camera to your eye has been a longstanding indication that you are about to take a photograph, and people notice this even out of the corner of their eyes. Using a tilting LCD screen from waist level helps a lot there. Also, looking elsewhere while taking the photo adds to your stealth. I've even raised the GRD III to my ear as if I'm talking on a phone, and taken photos of things to the side. The Fuji X10 and X100 can take photos that almost no one notices because of their very quiet startup, focusing and shutter sounds.
Some techniques I have found useful for remaining discreet:
- if your camera has any kind of noticeable startup noise, turn the camera on while holding it in your lap, or behind your leg. Anywhere that is out of sight is best. Don't hold the camera up to your face while turning it on.
- as an adjunct to the above, learn to shoot in postures that are not normally associated with camera usage. Look like you're just sitting there, or doing something other than taking a photo. Learn to shoot from the hip, and do not look at the subject. Don't raise the camera to your face unless you have to.
- If you're walking, look straight ahead and palm the camera, using your thumb on the shutter button instead of your index finger. If the camera is around your neck, you can shoot with the ball or joint of your thumb while looking as if you're just holding the camera securely.