图像中如何存在病毒？(How can a virus exist in an image?)

 我最近看过这个芬兰互联网安全专家的视频。 在第十一分钟的某个地方，他谈到隐藏在图像中的病毒，并在图像即将被显示时执行。 
 
 我想知道他们在技术上如何做这样的事情，我的意思是病毒是如何执行的 ，当图片应该显示出来，以及图片在某种程度上不会受到影响。 我以为电脑首先看看扩展，然后用适当的程序打开它，让程序自己工作（而且我不希望定期的图像查看器能够在其本身内运行病毒）。 显然这样做不行，但没有人问我可以帮助我。 
 
 有谁知道他们如何做到这一点呢？ 非常感谢你。 

I have recently watched this video of a Finnish internet security expert. Somewhere around eleventh minute, he talks about a virus which is hidden in an image and executes when the image is about to be displayed.
 
I am wondering how do they technically do such a thing, I mean how come the virus is executed, when the picture should be displayed and how come the picture is not compromised in some way. I thought the computer first looks at the extension, then opens it with appropriate program and lets the program work itself (and I don't expect regular image viewer to be able to run a virus within itself). Obviously it doesn't work like that, but no one I asked could help me out with this.
 
So does anyone know how do they do this, the principle? Thank you very much.

原文：https://stackoverflow.com/questions/9675941