Simple random image

random_image.php

<?php
function randomImage(int $width, int $height)
{
    $image = imagecreatetruecolor($width, $height);
    for($row = 1; $row <= $height; $row++) {
        for($column = 1; $column <= $width; $column++) {
            $red = mt_rand(0,255);
            $green = mt_rand(0,255);
            $blue = mt_rand(0,255);
            $colour = imagecolorallocate ($image, $red , $green, $blue);
            imagesetpixel($image, $column - 1 , $row - 1, $colour);
        }
    }

    header('Content-type: image/png');
    return imagepng($image);
}

Example result