observation - How was an infrared picture of the entire universe taken?

As other people said, what you see in that picture is a mosaic of images, centered in our Galaxy, produced with WISE observations in infrared light. Astronomers have used a projection method, called Aitoff, to project the spherical sky into a 2-dimensional map.

For a more detailed explanation of the image, please follow this link:

http://wise.ssl.berkeley.edu/gallery_thesky.html

HTH,

Germán.

PS: Sorry that my reputation doesn't allow me to put more than two links.