EDIT to add to previous post:
"If image retention occurs from stationary images (non-flickering), like the Windows taskbar, then the panel is defective or the firmware is defective (e.g. a firmware bug that accidentally disables the protective inversion algorithms -- e.g. voltage-polarity inversion stops occuring)."
As far as the panel voltage inversion logic is bug-free, static images never produces burn-in on a correctly functioning LCD. The voltages are thus always perfectly balanced for static stationary images.
It's when you use special synchronized flicker patterns (BFI, 3D glasses, synchronized flicker patterns), that this causes voltages to go out-of-sync and builds up to a positive-voltage buildup or a negative-voltage buildup (creating temporary image retention).
Buggy LCDs sometimes had a situation where the firmware accidentally disabled voltage inversion during some situations (especially out-of-range timings), in which case, static images will show retention behaviors. However, it is eraseable by a proportionate countermeasure. If retention appears only for a few minutes, it can disappear in only a few minutes. If you let retention become worse for several days, it can take several days to fully erase.
Image Retention: Buggy LCD Panel Test
(A) Test a static image for a few minutes
(B) If no image retention, continue to long test
(C) Test a static image for a few hours
(B) If no image retention, you're good!
If you get image retention, then pixels are not correctly swapping voltages. Do an RMA or firmware upgrade, which will sometimes fix this type of issue. LCDs should never do this.
Image Retention: Normal LCD Inversion Logic Sensitivty Test
And if you're picky about sensitive retention from flicker patterns (if you need to use BFI or 3D glasses)
(A) Test flicker image for few minutes such as www.testufo.com/ghosting ... keep the tickmarks in the same location
(B) Now suddenly display a full screen solid-gray field (e.g. 50% gray), or go fullscreen and drag ghosting bar up/down out of the way, look for retention in solid midshade color. Tickmarks (Sync Track) would have image retention
(C) If image retention, panel is sensitive. Drain pixel static electricity buildup via playing highly active full screen video for at least roughy 1x to 4x+ you displayed the flicker pattern for.
RMA usually won't fix this type of issue, panels will typically have the same image retention velocity.
This is largely simply a static electricity buildup behavior instead of a damaged pixel behavior (Caveat: If you defeated the inversion circuit continuously for a long period like weeks or months continuously, it's possible for the charge to permanently imprint. (So you don't want to display a frame-seqeuential Stereoscopic 3D Glasses Image as your screensaver!).