Select up to 12 images when you're in any view and open Survey mode to see them all at once. Survey mode is a great tool to compares images side by side.

To open Survey mode, click on the icon as shown in the screenshot below or hit (N) to open and (esc) to dismiss. Make sure you have the images that you want to compare highlighted before you hit N.

By default it will enter the image compare view

To compare faces from up to 6 images at once, select multiple images and open up Survey mode and click on the face icon as shown below.

To view this mode directly, click on the face icon or use (Shift + N) and (esc) to dismiss it.

To remove any images from the survey mode, click on the icon as shown below or press (,)

If you want to compare images and there are more than 12 you've selected, the extra images highlighted will show in the bottom right of survey mode as a number in a grey box. To compare all of the images you had highlighted, you'll have to remove some of the images from view to add more in. You can click , (comma) to remove an image from your Survey view and you'll notice that that will bring the next one in for you (the number on the grey square should decrease as you do this.