Question: What is The Persistence of Memory an image of?
About the article "The Persistence of Memory", section "Description".

Candidate passages:
The two main components of iconic memory are "visible persistence" and "informational persistence".
The first is a relatively brief (150 ms) pre-categorical visual representation of the physical image created by the sensory system.
This would be the "snapshot" of what the individual is looking at and perceiving.
The second component is a longer lasting memory store which represents a coded version of the visual image into post-categorical information.
This would be the "raw data" that is taken in and processed by the brain.
A third component may also be considered which is "neural persistence": the physical activity and recordings of the visual system.
Neural persistence is generally represented by neuroscientific techniques such as EEG and fMRI. 
Information persistence represents the "information" about a stimulus that persists after its physical offset.
It is "visual" in nature, but not "visible."
Sperling's experiments were a test of informational persistence.
Stimulus duration is the key contributing factor to the duration of informational persistence.
As stimulus duration increases, so does the duration of the visual code.
The non-visual components represented by informational persistence include the abstract characteristics of the image, as well as its spatial location.
Due to the nature of informational persistence, unlike visible persistence, it is immune to masking effects.
The characteristics of this component of iconic memory suggest that it plays the key role in representing a post-categorical memory store for which VSTM can access information for consolidation.  
Visible persistence is the phenomenal impression that a visual image remains present after its physical offset.
This can be considered a by-product of neural persistence.
Visible persistence is more sensitive to the physical parameters of the stimulus than informational persistence which is reflected in its two key properties.
:  The duration of visible persistence is inversely related to stimulus duration.
This means that the longer the physical stimulus is presented for, the faster the visual image decays in memory.
The duration of visible persistence is inversely related to stimulus luminance.
When the luminance, or brightness of a stimulus is increased, the duration of visible persistence decreases.
Due to the involvement of the neural system, visible persistence is highly dependent on the physiology of the photoreceptors and activation of different cell types in the visual cortex.
This visible representation is subject to masking effects whereby the presentation of interfering stimulus during, or immediately after stimulus offset interferes with one’s ability to remember the stimulus.
Different techniques have been used to attempt to identify the duration of visible persistence.
The Duration of Stimulus Technique is one in which a probe stimulus (auditory "click") is presented simultaneously with the onset, and on a separate trial, with the offset of a visual display.
The difference represents the duration of the visible store which was found to be approximately 100-200 ms. Alternatively, the Phenomenal Continuity and Moving Slit Technique estimated visible persistence to be 300 ms.
In the first paradigm, an image is presented discontinuously with blank periods in between presentations.
If the duration is short enough, the participant will perceive a continuous image.
Similarly, the Moving Slit Technique is also based on the participant observing a continuous image.
Only instead of flashing the entire stimulus on and off, only a very narrow portion or "slit" of the image is displayed.
When the slit is oscillated at the correct speed, a complete image is viewed. 
  "The Persistence of Memory" (2004)  
Persistence techniques.
System images.
Using system images is the simplest persistence strategy.
Notebook hibernation is an example of orthogonal persistence using a system image because it does not require any actions by the programs running on the machine.
An example of non-orthogonal persistence using a system image is a simple text editing program executing specific instructions to save an entire document to a file.
Shortcomings: State changes made to a system after its last image was saved are lost in the case of a system failure or shutdown.
Saving an image for every single change would be too time-consuming for most systems, so images are not used as the single persistence technique for critical systems.