Delphi PNGImage - Image transparency is not pure

I am using PNG images as main image resource in my application. Since im not using Delphi XE7, i downloaded PNGImage lib and included it in project. I load images like this:

Form.image.Picture.LoadFromFile(PAnsiChar('\background.png'));

Image has transparent and semi transparent pixels on its border. The problem i get is that transparent pixels are filled with part of my desktop with currently opened windows.

Additionally, form has this properties:

BorderStyle: bsNone; TransparentColor: true; TransparentColorValue: clBlack; Visible: false;

Can this be fixed somehow or it is how delphi deals with transparency?