You might be able however integrate with my AI Horde endpoint for NSFW checking between nginx and Lemmy.

https://aihorde.net/api/v2/interrogate/async

This might allow you to detect NSFW images before they are hosted

Just send a payload like this

curl -X 'POST' \
  'https://aihorde.net/api/v2/interrogate/async' \
  -H 'accept: application/json' \
  -H 'apikey: 0000000000' \
  -H 'Client-Agent: unknown:0:unknown' \
  -H 'Content-Type: application/json' \
  -d '{
  "forms": [
    {
      "name": "nsfw"
      }
  ],
  "source_image": "https://lemmy.dbzer0.com/pictrs/image/46c177f0-a7f8-43a3-a67b-7d2e4d696ced.jpeg?format=webp&thumbnail=256"
}'

Then retrieve the results asynchronously like this

{
  "state": "done",
  "forms": [
    {
      "form": "nsfw",
      "state": "done",
      "result": {
        "nsfw": false
      }
    }
  ]
}

or you could just run the nsfw model locally if you don't have so many uploads.

if you know a way to pre-process uploads before nginx sends them to lemmy, it might be useful