Comment by Xamayon

Their crawler doesn't identify itself, here's what one of the log entries looks like:

x.x.x.176 - - [16/Apr/2021:13:xx:xx -0400] "GET /search.php?url=hxxps://i.imgur.com/xxxxxxx.xxx HTTP/1.1" 429 357 "hxxps://4archive.org/board/b/thread/xxxxxxxxxxx" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/86.0.4240.75 Safari/537.36"

We blocked that one successfully, but the same image was used to search iqdb.org, bypassing their filter and resulting in the current prolonged downtime. Their host took the site down ~3 days ago, and has not been responding to any tickets since...