I'd like to tell an older person, how to open images from his USB stick or SD card and continue to the next images in the containing folder very easy.
On Windows, he can plug in the memory device, wait until an explorer opens and double click an image. Then he can use the arrow keys left/right to show the other images in this directory.
On OS X, you can open a finder after attaching, double click an image but in preview.app, which opens then, you can not navigate to the other pictures. Another option is to select all images (CMD + A) and drag and drop them to the preview.app-icon in the dock. But thats very error-prone if he accidentally rise the mouse button while dragging.
It's not a solution to import the photos in any application like iPhoto, Lightroom or so for this case, because the Mac is just for viewing them. They are always imported later on another computer. I'm afraid of the suspense, which files are the most up to date ones or to clean his Mac every two weeks.
I'd like to have a simple tool for that, I can install. Ideally, it will pre-load the next pictures I can navigate to, to speed things up. Windows does so.