What is actually at risk
- The sensor, from sustained exposure to concentrated sunlight.
- The shutter curtains, which sit in the same focused beam before the exposure begins.
- The autofocus sensor, named alongside the others in the accepted answer.
- Your eyes, if the camera has an optical viewfinder — the same concentration reaches them through it.
When it matters and when it does not
- Long focal lengths concentrate the sun into a small, intense spot. This is the case that causes damage.
- Wide angles spread the same energy over a large area, and one answer stated plainly that having the sun in frame at wide angles does not normally harm anything.
- A low sun is much weaker, because its light passes through far more atmosphere than when it is overhead.
- Duration matters as much as focal length. A frame taken with the sun in it is different from leaving the camera pointed at it.
The dissenting experience
One contributor reported never seeing this happen with compact cameras, across four bodies used for time-lapse work running to hundreds of thousands of exposures each. It is worth including because it is consistent rather than contradictory: a small compact has a short focal length and a tiny lens, which is the configuration the other answers describe as low risk. It supports the focal length explanation rather than undermining it.
If you want to photograph the sun
- Use a strong neutral density filter. One answer described using one cutting the light by a factor of several hundred.
- One answer made the practical observation that if the sun is bright enough to be a hazard, it is also too bright to give a usable exposure — so the filter is needed for the picture as well as for the camera.
- Solar eclipse and direct solar photography have their own filter requirements that this thread does not cover.