image magick will not upload any image larger than 100KB

<?php 
 
    //function to upload image and check type
	
	 function upload_image($file_name) {
		   if (isset($_FILES[$file_name]))  {
		   //validate the type. Should be JPEG or PNG.
		   $allowed = array('image/pjpeg', 'image/jpeg', 'image/JPG', 'image/X-PNG', 'image/PNG', 'image/png', 'image/x-png');
		   if (in_array($_FILES[$file_name]['type'], $allowed)) {
			   return $image_type = "ok";  }
		   else 
		     { return $image_type = "error";  }
	   }
	 }  
	 //end of upload image function
							
 
 
 
    //function to reduce and move image - receives path for permanent location
     
	 function move_image($file_name, $full_path, $short_path, $image_width)  {
		 // find ext
       $ext = end( explode('.', $_FILES[$file_name]['name']) );
	  
	   //get timestamp
	   $stamp = mktime();
		
	   //set the file location
	   $new_image = $full_path.md5($_FILES[$file_name]['name']) . $stamp .'.' .$ext;
	   $stored_name = $short_path.md5($_FILES[$file_name]['name']) . $stamp .'.' .$ext;
		 
	   $original_image =  $_FILES[$file_name]['tmp_name'];
	   
	   $size = GetImageSize($original_image);	  	
	   	   
	   //default max width is 300 unless specific width passed to function   
	   $max_width = "300";
	   $max_height = "300";
	   If ($image_width) {
		   $max_width = $image_width;
		   $max_height = $image_width;}
		   	   	       
	   exec("convert -size {$size[0]}x{$size[1]} $original_image -thumbnail $max_widthx$max_height $new_image");	       
	   
	   return $stored_name;	   }
   ?>

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