First I wanted just to answer "of course not, no more than looking at a photo of the sun. But then I thought it would be good to differentiate a bit more.I think the most dangerous thing is to look at the sun through something that contains lenses, or concave mirrors, such as a telescope. This can burn your retina instantaneously while it will take at least some seconds, if not more, to harm your eyes permanently by looking at the sun directly. The next bad thing after looking at the sun directly is looking at it through a window or other flat glass, or in a flat mirror. The glass takes some of the light away and the mirror does not reflect all, but as much as possible - that's what a mirror is for.It might also be bad to look at a bright sunlit surface that isn't a mirror, like a water surface or snow or white paper. Snow blindness is known to exist but as far as I know it's a matter of hours rather than seconds. I have had troubles seeing something indoors after sitting in the sun and reading a book with bright white pages, but I don't think there was any permanent harm done.A television or computer screen is not reflecting any sunlight (you are not supposed to even let the sun shine on it, otherwise there will, of course, be a reflection but very weak), it has a light source of its own. This light source is not supposed to be harmful, but that doesn't necessarily mean that none of them are really able to do harm if you put the brightness to the maximum. But in this case an all-white screen will be much worse than a small white spot representing the sun. You are more likely to harm your eyes reading this message on white background than looking at a lot of photos of suns, explosions and lasers on the same computer screen. So now what about cinema or beamer? (let's consider an all-white picture at once rather than a picture of the sun). The screen is surely brilliant white and the lamp is surely very strong. But I suppose it's still weaker (or at least not MUCH stronger) than the sunlight even through the window, or you would't have to darken the room to watch the picture. And then, you are much more likely to walk several hours through a sunny winter landscape than to stare at a blank white cinema screen for hours... Only NEVER look INTO the lamp! That might be worse than the sun after all!