When overlaying a Watermark watermark in opencart with a png extension on a product with a png extension, the watermark paints over the entire area, how to solve it?

Question

CMS

When overlaying a Watermark watermark in opencart with a png extension on a product with a png extension, the watermark paints over the entire area! How to solve this problem and is it really possible to do it? With other extensions everything is ok!
I found how to make an overlay and so that it is displayed, but the background is now not transparent, but black
, this is joxi.ru/4Ak8RnbC5p6prq , namely the line imagealphablending($this->image, false);
replaced with imagealphablending($this->image, true); everything worked...
How to make the black background transparent? If you have any ideas please share! THX!