When using helm-find-file you can use helm-follow-mode to cause images to show themselves as you move over them, replacing the need to start up some other program to preview images. The shortcut for that while within helm-find-file is C-c C-f. By default, you will be ejected from the follow mode as soon as you move over a non-image file. The following customizatoin will give it a little more tolerance: (setq helm-follow-input-idle-delay 0.