JPEG-LS

import magic
# Libmagic may identify the standard JPEG SOI and mistakenly label this as 'image/jpeg' without deep marker inspection
print(magic.from_file('scan.jls', mime=True))

const fs = require('fs');
// Manually detecting the JPEG-LS SOF55 marker directly following the SOI marker
const buffer = Buffer.alloc(4);
const fd = fs.openSync('scan.jls', 'r');
fs.readSync(fd, buffer, 0, 4, 0);
fs.closeSync(fd);
const isJpegLS = buffer[0] === 0xFF && buffer[1] === 0xD8 && buffer[2] === 0xFF && buffer[3] === 0xF7;
console.log(isJpegLS);

import (
    "bytes"
    "net/http"
)
// http.DetectContentType will incorrectly return 'image/jpeg' due to the FF D8 prefix.
// Custom detection must verify the FF F7 (SOF55) marker.

// Standard PHP setups will likely return 'image/jpeg' because it shares the same generic FF D8 file signature.
$mime = mime_content_type('scan.jls');
echo $mime;