A bot strips away all spaces and letters that aren't A, T, C or G, then treats the rest like a genetic sequence and checks it against some database.
Presumably, it runs through many terabytes of data for each comment, as the Gallinula chloropus alone has about 51 billion base pairs, or some 15 GiB. The Genome Ark DB, which has sequences of two common moorhens, contains over 1 PiB. I wonder if a bored sequencing lab employee just wrote it to give their database and computing servers something to do when there is no task running.
No, I won't download the genome and check how close the "closest match" is but statistically, 93 base pairs are expected to recur every 2^186^ bits or once per 10^40^ PiB. By evaluating the function (4-1)^m^ × mℂ93 ≥ 4^93^ ÷ (pebi × 8), one can expect the 93-base sequence to appear at least once in a 1 PiB database if m ≥ 32 mismatches or over ⅓ are allowed. Not great.
This assumes true randomness, which is not true of naturally occuring DNA nor letters in English text, but should be in the right ballpark. Maybe fewer if you account for insertions/deletions.
What kind of image is it? Reducing the number of colors in a PNG is usually inferior to JPEG compression. It can be OK for screenshots of texts and simple drawing but otherwise you're better off with lossy JPEG or WebP.
Some instance admins don't even use the built-in
pict-rsserver so media cannot be uploaded natively at all.Some only allow month-old accounts to post images up to 500 kiB.
Others leave the limits on the relatively high defaults: 10 MiB per file and up to 900 frames for soundless animation/video, which must be in WebM format and VP9 codec (or it will need to be reencoded, which usually fails because of the short timeout). It's easy to use
ffmpegor HandBrake to create low-bitrate 30-second HD videos that fit but the limits are not visible to users and even the defaults are nowhere to be found in Lemmy documentation, I had to read the source code.