With the stock Gallery app, how can I open an arbitrary image file by specifying its filesystem path? I would like to know whether it is possible to open an arbitrary image file with the stock Gallery app (as distributed with the Samsung Galaxy SIII) by navigating the filesystem and drilling down the path to the image and clicking on the image to be opened. It seems to me that the only place it allows its users to select files from are the folders found under /storage/emulated/0/DCIM (normal pictures), the folders found under /storage/emulated/0/Pictures (screenshots), /storage/emulated/0/PhotoEditor for pictures created with the Samsung Photo Editor which can be installed from the Gallery application by clicking on the edit picture icon on the top-right-hand-side when viewing a picture, /storage/emulated/0/Download for images downloaded from the web via a web browser, and other albums taken from Google Picasa Web.

Right now I'm guessing that when the stock Gallery application is opened, it just traverses the entire filesystem and for each directory which it finds which contains an image it displays the directory name along with the last image in such directory (and switches to a grid view for the images in that directory if clicked).

In any case, I would like to know if there's an alternative way to open an image directly form the stock Gallery app, e.g. Gallery could launch a file explorer application upon request once a picture is selected? Thanks.
You're not limited to using the Gallery app to view your images.  I've loaded a file explorer app called ES File Explorer File Manager that allows me to traverse not only the local content of my phone, but, also, any network drives I may have access to.  When selecting an image file, you are presented with a list of programs that are registered to open the image.  The program can use the Gallery app, or, its own built in image viewer, or, any other registered image viewer.