It is a natural responding to blink eyes when taking picture. This is causes by the flash from Camera. And we blink eyes to shield the our eyes from such flash light. And it is really hard to avoid blink eyes when take photos. But to get a beautiful pictures, you shall try your best to keep your eyes open. Or you can ask a photographer takes the picture without having the 'click' (mirror-up in SLR/DSLR) that may help you. Or, you can wearing sunglasses when you take pictures if you can. It will give you a cool shot.
Well,in terms of this situation,u might as well try to get ur eyes watery.U may don't know that watery eyes can prevent ur eyes from blinking very soon and effectively.However,although this is very useful,watery eyes can also make u feel uncomfortable.There is also another good way,that is,u can just look at somewhere else instead of looking at the camera.U know,the only reason that u will blink ur eyes when taking pictures is cuz that the flash of ur camera can hurt ur eyes quite easily.