PHP script to render a single transparent pixel (PNG or GIF)

Question

Transparent 1x1 PNG:

header('Content-Type: image/png');
echo base64_decode('iVBORw0KGgoAAAANSUhEUgAAAAEAAAABAQMAAAAl21bKAAAAA1BMVEUAAACnej3aAAAAAXRSTlMAQObYZgAAAApJREFUCNdjYAAAAAIAAeIhvDMAAAAASUVORK5CYII=');

Transparent 1x1 GIF:

header('Content-Type: image/gif');
echo base64_decode('R0lGODlhAQABAJAAAP8AAAAAACH5BAUQAAAALAAAAAABAAEAAAICBAEAOw==');

In PHP 5.4 and higher it is possible to use hex2bin, which is roughly two times faster than base64_decode (tested with the blank GIF file below). The code to output images would be:

Transparent 1x1 PNG:

header('Content-Type: image/png');
die(hex2bin('89504e470d0a1a0a0000000d494844520000000100000001010300000025db56ca00000003504c5445000000a77a3dda0000000174524e530040e6d8660000000a4944415408d76360000000020001e221bc330000000049454e44ae426082'));

Transparent 1x1 GIF:

header('Content-Type: image/gif');
die(hex2bin('47494638396101000100900000ff000000000021f90405100000002c00000000010001000002020401003b'));

You can easily convert base64 encoded data into hexadecimal:

echo bin2hex(base64_decode($data));

Or a file:

echo bin2hex(base64_decode(file_get_contents($filename)));

However, using the native PHP escape method suggested by @Lukas Liesis is the fastest, about 12.5 times faster than base64_decode, according to my benchmark. And it would work with virtually any version of PHP. Here are the code snippets:

Transparent 1x1 PNG:

header('Content-Type: image/png');
die("\x89\x50\x4e\x47\x0d\x0a\x1a\x0a\x00\x00\x00\x0d\x49\x48\x44\x52\x00\x00\x00\x01\x00\x00\x00\x01\x01\x03\x00\x00\x00\x25\xdb\x56\xca\x00\x00\x00\x03\x50\x4c\x54\x45\x00\x00\x00\xa7\x7a\x3d\xda\x00\x00\x00\x01\x74\x52\x4e\x53\x00\x40\xe6\xd8\x66\x00\x00\x00\x0a\x49\x44\x41\x54\x08\xd7\x63\x60\x00\x00\x00\x02\x00\x01\xe2\x21\xbc\x33\x00\x00\x00\x00\x49\x45\x4e\x44\xae\x42\x60\x82");

Transparent 1x1 GIF:

header('Content-Type: image/gif');
die("\x47\x49\x46\x38\x39\x61\x01\x00\x01\x00\x90\x00\x00\xff\x00\x00\x00\x00\x00\x21\xf9\x04\x05\x10\x00\x00\x00\x2c\x00\x00\x00\x00\x01\x00\x01\x00\x00\x02\x02\x04\x01\x00\x3b");

Creating such a string is easy with regular expressions (as it's done once, it doesn't have to work fast):

echo preg_replace('/../','\\x\0',bin2hex($data));

Or from a file:

echo preg_replace('/../','\\x\0',bin2hex(file_get_contents($filename)));

To answer some people's questions:

You must echo the contents of an image. The Header only shows that are you are returning an image to the browser, instead of normal text. So if you only return a header, it's just a header - no data. However, print out data of an image and done, you just sent an image :)

Reading a file is not good, it could work, but it's better to return raw data like shown in main answer by Sjoerd. This way, you save time and server load not having to process a read operation. Reading from disk is a slow task. Over time, reading from disk has increased in speed with SSD disks, but still, No I/O to disk is better.

I had this code even without base64 decode, but this image has white color:

header('Content-Type: image/gif');
// 1x1px white gif
die("\x47\x49\x46\x38\x37\x61\x1\x0\x1\x0\x80\x0\x0\xfc\x6a\x6c\x0\x0\x0\x2a\x0\x0\x0\x0\x1\x0\x1\x0\x0\x2\x2\x44\x1\x0\x3b");

Maybe someone knows how to convert any file to such data string?

header('Content-Type: image/gif');
printf('%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%', 71, 73, 70, 56, 57, 97, 1, 0, 1, 0, 128, 255, 0, 192, 192, 192, 0, 0, 0, 33, 249, 4, 1, 0, 0, 0, 0, 44, 0, 0, 0, 0, 1, 0, 1, 0, 0, 2, 2, 68, 1, 0, 59);