With this script you can split a super long image in how many parts you want, and stack them. Like a long ecg chart: https://i.imgur.com/ZlwMNRz.png

PHP image cut split in parts stack on top .php

<?php
$source_path = 'super-long-image.png';
$destination_path = 'new-image.png';
$parts = 3; // in how many parts you want to split the image

$source = imagecreatefrompng($source_path);
$width = imagesx($source);
$height = imagesy($source);
$newWidth = $width / $parts;
$newHeight = $height * $parts;
$splitWidth = $width / $parts;
$splitHeight = $height;

$image = imagecreatetruecolor($newWidth, $newHeight);
for ($i = 0; $i < $parts; $i++) {
    imagecopy(
        $image, // destination img
        $source, // source img
        0, // destination X
        $i * $splitHeight, // destination Y
        $i * $splitWidth, // source X
        0, // source Y
        $splitWidth, // split source width
        $splitHeight // split source height
    );
}

imagepng($image, $destination_path);
imagedestroy($image);
imagedestroy($source);