UPDATE: Picasa is no longer being developed by Google who abandoned it in 2016. However, as written in other articles, if you need a program not only to view images and photos but also to manage collections and albums, the choice the better the powerful software, in In your language, Google Picasa.

Personally, I think the default image viewer in Windows is bad and that the best program to browse and see photos on your pc is IrfanView with which you can view images by going back and forth with the space bar. On Windows, when you click on an image file, it is displayed with the default program which, by default, is the Windows image viewer. This same zoom effect is available on some websites where, by clicking on a photo, the page darkens while remaining in the background and, with a fade effect, you can see the large image. A nice feature of Mac computers is that it allows you to open preview images, without opening them in a program but simply by enlarging the photo with a zoom, directly from the desktop.

Picasa photo viewer only