Upload HTTP error frequently after patch 9767 v2

Question

After applying patch SUPEE-9767 v2, i've often got an error like this

but sometimes the uploading process works fine, but for some images when i try to upload it, it shows http error

after doing some log, turns out the error comes out from

app/code/core/Mage/Core/Model/File/Validator/Image.php

in validate() function there's code like this:

$img = imagecreatetruecolor($imageWidth, $imageHeight);
imagealphablending($img, false);
imagecopyresampled($img, $image, 0, 0, 0, 0, $imageWidth, $imageHeight, $imageWidth, $imageHeight);
imagesavealpha($img, true);

when i remove those code, all my file can be uploaded, i don't know why these functions above won't work form some of images

Answer 1

This question may have been answered in the past. Please review the responses. https://stackoverflow.com/questions/18994648/magento-upload-http-error

I think the issue may be in the size limits.