Do not expect to see the image in full 3D immediately. It can take several seconds to a minute looking at one stereo pair for a new observer to see stereoscopically, which is not surprising considering the complex brain processes involved. If the observer says "Oh yes, very nice," we know he has not seen in 3D. When he suddenly says "Oh my goodness, that is amazing!" his stereo vision is intact. If he tries to look around near objects to see far objects, stereo vision is definitely in action.
The skill to see stereoscopically is learned in infancy, before the age of 3:
The 3D world is learned as infants reach into it and find objects in different places. Later they crawl into it and bump into all kinds of pleasures and disasters. By using all their senses, which agree with each other about the world, infants learn about the third dimension. The visual, stereoscopic impression of the 3D environment arose from combining all the senses together and coming to realise our two eyes are supreme at giving exquisite detail about where objects sit in relation to us and to each other.
The 1/6 children who fail to develop stereoscopic vision still know about a 3D world from all their other senses, and almost have the detailed knowledge provided by stereo vision, because the very powerful motion 3D is still available to them.
The 1/3 who cannot see 3D properly from two flat images separately presented to each eye can still function very well in the real world and only meet difficulty when they see 3D movies or the pictures on this web site and end up:
Soon 3D television will be available and only gentle 3D depth will be possible for a significant proportion of the population.
Are 3D pictures dangerous for children? I personally doubt there is any problem, but have no evidence either way.
Problems viewing 3D television
3D TV (stereoscopic television) has hit the shops and there is no consensus on the best way to see it.
I can tell you how I see stereoscopically now, but there will be no attempt to review the mass of possible methods. For a start, consumers will not tolerate anaglyphs. 3D TV must be full colour, high definition. Many naive people refuse to wear glasses to see 3D (Or claim they will never put those "geek goggles" on.) Lenticular screens do show 3D with no glasses but you have to sit in exactly the right place or it fails. Ther can be more than one sweet spot, but lenticular is not ideal for family TV or for people who insist on wriggling about while watching TV.
At this time, it is more important to make and store 3D images (and movies) in a form that can later be converted to whatever is needed to view them. The conversion is best done in the viewer's own computer, so that he can download stereo content and change it to whatever form is needed by his 3D viewing system. This means providing two images, one for each eye.
It is better if the image pair is in a form which can be seen in 3D without doing anything to them, and in my view that is cross-eye stereo format. Any size stereo pair can be seen cross-eyed but only small versions can be seen with parallel eyes, unless a mirror or prism viewer is used. Anaglyphs are much more popular on the internet (review the Flickr stereo groups) but anaglyph is a very bad choice for storing 3D content, because the colour is destroyed, while a stereo pair retains all colours. 3DTV will fail if it is based on anaglyphs. Cross-eye pairs can be tranformed to any viewing system on the fly by using the free program: StereoPhotoMaker (SPM).
Consumers will demand full colour stereo with High Definition (1920x1080 pixels, aspect ratio 16:9 or 1.8. Even higher pixels counts are already essential for 3D movies. The wide screen aspect ratio is now standard for 2D TV and modern computer monitors in the shops are all at least 16:10 aspect ratio (8:5, 1.6). Most amateur stereoscopic photographers are already out-dated by not providing letter-box shaped 3D images.