There are many options to view stereoscopic image pairs.

• There are two unassisted methods to view image pairs.

  • Parallel viewing. The images are placed the way they would be with a viewer. The right image is in front of the right eye. Since it's very difficult to separate convergence from focus, I've successfully used this method once. This works only with small images with the centers only a few inches apart.

  • Cross-eye viewing. The right image is placed on the left side. The eyes are crossed so the right eye looks at the right image (which is on the left side). The left eye will look at the left image (which is on the right side). This works for arbitrarily large images, limited by your ability to cross and focus your eyes. This is far easier than parallel viewing, since most people are able to cross their eyes. However, if images are in the wrong order, the effect will be wrong and may be disorienting.

• If you're viewing digital images, you can try making wigglegrams. They are basically just animated images that flip between views. If you don't need the GIFs, you can just switch between images in an ordinary image viewer. With prints, you can try making a flip book.

  

• You can try creating anaglyphs. They require using special red/blue or red/cyan glasses.

  

• With the advent of Google Cardboard, phone VR viewers have become very common. I have even seen them in discount clothing stores, dollar stores, and thrift stores. You would still need to find an app to display the images.

  • There are viewers that are little more than lenses in a frame. If you'd prefer this type of viewer, you can try adding search terms "compact", "portable", "folding", etc.

  • Strong reading glasses may work. Most Google Cardboard viewers use planoconvex lenses, which function the way reading glasses do. (I haven't tried though.)

  • Loreo makes viewers that predate Google Cardboard. They use prisms instead of planoconvex lenses, so might work better with larger images.

• Special hardware, glasses, etc.

  • There are some televisions and displays that allow free viewing stereoscopic pairs. Some notable devices with 3D displays:

    • Nintendo 3DS portable gaming system.
    • FujiFilm Real 3D W1 and W3 cameras.
    • List of 3D capable phones on Wikipedia.

  • There are systems that use shutter glasses to alternately block each eye while flipping between images.

Software that may be of interest...

• Stereo Photo Maker – Windows and Mac OS.
• 3DSteroid – Android.