JPG JPEG File Interchange Format

SIGNATURE = bytes.fromhex("ffd8ff")
OFFSET = 0

def is_jpg(path: str) -> bool:
    with open(path, "rb") as f:
        f.seek(OFFSET)
        head = f.read(len(SIGNATURE))
    return head == SIGNATURE

const SIGNATURE = [0xff, 0xd8, 0xff];
const OFFSET = 0;

// bytes: a Uint8Array / Buffer holding the start of the file
export function isJpg(bytes) {
  return SIGNATURE.every((byte, i) => bytes[OFFSET + i] === byte);
}

package fileid

import "bytes"

var isjpgSignature = []byte{0xff, 0xd8, 0xff}

const isjpgOffset = 0

func IsJpg(b []byte) bool {
	end := isjpgOffset + len(isjpgSignature)
	if len(b) < end {
		return false
	}
	return bytes.Equal(b[isjpgOffset:end], isjpgSignature)
}

const SIGNATURE: &[u8] = &[0xff, 0xd8, 0xff];
const OFFSET: usize = 0;

fn is_jpg(bytes: &[u8]) -> bool {
    bytes.get(OFFSET..OFFSET + SIGNATURE.len()) == Some(SIGNATURE)
}

<?php
$signature = "\xff\xd8\xff";
$offset = 0;

function is_jpg(string $bytes): bool {
    global $signature, $offset;
    return substr($bytes, $offset, strlen($signature)) === $signature;
}