There are two types of moderators for this forum: local moderators, (Melody, Alan, ...), and image-moderators, which is an image moderation service (probably) located in India.
The image-moderators only see the image and approve or block it based on predetermined criteria by the webmaster or administrator. For this forum, the typical blocked images include:
* Pornography (or any human nudity).
* Subjects that are generally considered gross, disgusting, or repulsive, such as those of diseased, mangled or decomposing remains of humans or animals, and those that are scatological in nature.
* Destructive weaponry, such as guns, knives, and swords –these may include fictional weapons such as ray-guns or laser-swords. Ironically though, you probably could post mages of atomic bombs, nerve-gas canisters, and deadly biological agents without impediment.
* Subjects depicting racism, hate-speech, and violence.
Until recently math related images were not blocked. These images are not intentionally blocked; they are passively blocked. A probable cause for this nuance is a Covid-related reduction in personnel at the image moderation service company. The image-moderators have about two minutes to approve or block an image. For this form, the image is processed though a switchable proxy container before it is displayed on the thread. The code for the switch is reported/{null}. The {null} allows the image to display normally. If a decision is not made in the allotted time the default is “report” and this displays a scrambled image.
(The original image is not scrambled, which is why I could reproduce the image in this post.)
Originally, the form’s local moderators had the option to override a blocked image. This option disappeared in a subsequent update. The form’s administrator, Herr Massow, periodically resets these block images
Additional notes:
On the questions (contents) page, questions are abbreviated, and those with an image are indicated by an icon; the actual image is not displayed. The same abbreviated content is used in the profile pages for questions by members.
On the answers (index) page, answers that have an image are displayed. On the index page, these images are displayed, even if the image is blocked on the thread. This content is also displayed in the profile answers page for members. This content on is not blocked on the profile answer page, and never has been.
Here is an example:
Here is a photo of knives with dried blood. 
This would definitely be blocked by the image moderating service; yet, it’s clearly visible in the answer (index) page.
--. .-
