I was very intrigued by the concept of bokeh after I saw this slide, so looked it up on the Internet and found a bunch of interesting stuff! Here is a very descriptive Wikipedia article describing bokeh in detail: https://en.wikipedia.org/wiki/Bokeh. Bokeh is normally defined as the way a lens renders out-of-focus points of light, and although it might not be ideal for rendering images in VR, it is actually often a desirable aesthetic quality for images to have! One can quantify the bokeh of a lens by looking at its circle of confusion (as described on the previous slide). Since the appearance of bokeh is heavily dependent on the lens and how it reacts to light in various ways, many companies have tried producing multiple varieties of lens in order to either reduce bokeh or enhance it in order to make pleasing images.
Bokeh can actually be simulated by convolving an image with a kernel that corresponds to the same image of an out-of-focus point source taken with a real camera. Some very advanced digital cameras also have bokeh features built-in. These features take several images with different apertures and focuses and then compose them afterward into one image. Another interesting factoid about bokeh - in 2009 some researchers from MIT Media Lab created barcodes using bokeh (which they called bokodes!). Apparently if one viewed the bokode using an ordinary camera focused at infinity, the resulting image would be large enough the scan the information in the barcode. Who said bokeh was a bad thing?
Personally, I love good bokeh. And I think portrait mode in iPhone can do a bokeh-like effect. More info: https://en.wikipedia.org/wiki/Bokeh
Adding the bokeh effect to a non-bokeh image is relatively simple: https://developer.apple.com/documentation/accelerate/vimage/adding_a_bokeh_effect