A simple script to process file uploads from Dropzone.js extension. Just call the function `uploadFile()` and add the desired params.

UploadDropzoneFile.php

<?php
/**
 * @var $file is an array with file data
 * @var $targetDir string with path to directory
 * @var $maxFileSize int with max Byte size
 * @var $_allowedFileTypes a comma separated string with all the allowed extensions
 */
function uploadFile(array $file, $targetDir, $maxFileSize = 100000, $_allowedFileTypes = '(jpg)')
{
	// create var from array
	$filename		= (isset($file['name']))		? $file['name'] : '';
	$filetype		= (isset($file['type']))		? $file['type'] : '';
	$file_tmpname	= (isset($file['tmp_name']))	? $file['tmp_name'] : '';
	$fileerror		= (isset($file['error']))		? $file['error'] : '';
	$filesize		= (isset($file['size'])) 		? $file['size'] : '';
	
	/**
	 * Get exension from File
	 *
	 * @var $filename string with the full file name
	 */
	function findExtension($filename)
	{
		if(is_string($filename))
		{
			$filename = strtolower($filename);
			$exts = split("[/\\.]", $filename);
			$n = count($exts)-1;
			$exts = $exts[$n];
			return $exts;
		}
		else
		{
			trigger_error('File name was not a string');
			print_r($filename);
			return false;
		}
	}
	
	// check extension
	$ext = findExtension($filename);
	// check if extension is allowed
	$allowedFiles = preg_match("/".$_allowedFileTypes."$/i", $ext);
	
	// setup errors
	// create checks and balances
	$err = array(
		'complete' => 'false',
		'is_error' => 'warning'
	);
	// maxsize == 100kB
	$err['message'] = ($filesize > $maxFileSize) ? "File is too large ($filesize). Please make sure your file is less than $maxFileSize" : null;
	// filetype == only $_allowedFileTypes
	$err['message'] = ($allowedFiles != true) ? "File format is incorrect ($filetype). Please make sure your image is JPEG." : null;
	if( isset($err['message']) )
	{
		if( $err['message'] !== null )
		{
			trigger_error($err['message']);
			return false; # stop function here
		}
	}
	
	// if the file extension is allowed
	if( $allowedFiles == true )
	{
		// setup target file
		$target_file = $targetDir . $filename;
		// move the file from tmp folder to target folder
		$move_file = move_uploaded_file($file_tmpname, $target_file);
		
		// if moved sucess
		if ($move_file)
		{
			$message = array(
				'complete' => 'true',
				'is_error' => 'success',
				'message' => 'Image uploaded successfully.'
			);
		}
		else
		{
			$message = array(
				'complete' => 'false',
				'is_error' => 'danger',
				'message' => 'Image NOT uploaded successfully.'
			);
		}
		return (json_encode($message));
	}
	else
	{
		trigger_error('Invalid file format');
		return false;
	}
}
// upload.php
if(isset($_POST))
{
	if( isset($_FILES) )
	{
		$upload = uploadFile(
			$_FILES['file'],	# file should be an array
			'_uploads/',		# target folder for upload
			125000,				# max upload size in Bytes (currently set to 1Mb) 
			'jpg,png,gif'		# allowed files should be separated by `,`
		);
		print_r($upload);
	}
	else
	{
		echo 'Incorrect data passed.';
	}
}
else
{
	echo 'Nothing to see here.';
}