Upload images → Arrange until the specified size → Save as a single image

<?php

// Image Height to Specify
$maxHeight=(int)$_POST['max_height'];

// Width of image to specify
$maxWidth=(int)$_POST ['max_width'];

// uploaded image
$image=$_FILES['image']['tmp_file'];

// Divided by /
$mimeType=explode('/',$_FILES['image']['type']);

if($mimeType[1]==='jpeg'||$mimeType[1]==='png'||$mimeType[1]==='gif'){

    // GD the uploaded image
    $functionName='imagecreatefrom'.$mimeType[1];
    $gdImage=$functionName($image);

    // image height
    $imageHeight=imagesy($gdImage);

    // image width
    $imageWidth=imagesx($gdImage);

    // GD for copy
    $result=imagecreateruecolor($maxWidth,$maxHeight);

    // Number of vertical copies (floor if not overhanging)
    $copyY=ceil($maxHeight/$imageHeight);

    // Number of horizontal copies (floor if not overhanging)
    $copyX=ceil($maxWidth/$imageWidth);

    // copy away
    for($y=0;$y<$copyY;$y++){
        for($x=0;$x<$copyX;$x++){
            imagecopy($result,$gdImage,$x*$imageWidth,$y*$imageHeight,0,$imageWidth,$imageHeight);
        }
    }

    // output the results of
    $outputFunctionName='image'.$mimeType[1];
    $outputFunctionName($result,'./output.'.$mimeType[1]);

}