How do I know what it is?

If you can change with a slider on your phone the amount of “bokeh blur” after you take a picture, you are seeing non-optical bokeh.

For the photo to be TTG-eligible, you have to move the (artificial) “aperture” slider to the highest number available — that is, you have to focus-maximize the photo.

(There are other ways to introduce non-optical bokeh blur to photos, but the advanced nature of those processes usually means that the photographer is well aware that the added blur is not optically produced.)

Non-optical blur always disqualifies a photo from TTG

Any blur that is executed by any non-optical means always disqualifies the result from TTG.

This disqualification obviously includes the increased blurring of backgrounds done using the “Portrait” setting on smartphones (described in the box above),

but it also includes any blur additions made using computer software, blur-adding filters placed in front of the lens, and any other means of adding “focus blur” (for “motion blur,” see the next box below).

Non-optical bokeh/fauxkeh is disqualified by TTG because there is no way to limit it from being carried to extremes

But optical blur is allowed by TTG

Any blur in TTG-qualified photographs can only be caused by optical means — i.e., by light passing through the lens.

This “allowable blur” includes out-of-focus areas rendered by the lens aperture setting, and it also includes motion blur (subject of course to sasibe limits) and panning/camera shake.

Summary

Apart from the effects of TTG's Allowable Changes, any post-exposure change to bokeh other than eliminating fauxkeh (see “Tip” above) — regardless of how convincing the result may look — always disqualifies a photograph from P2 and thus from TTG.

Besides the guide to focus and bokeh blur linked above, FAQs #1210–1214 also discuss bokeh blur