OCR doesn't working, all the characters recognized as dots

The extension is offering OCR, but after trying to recognize of few dozens of PDF documents (scans), no one character was recognized.
As you can see on the screenshot http://i.imgur.com/MDBkXWy.png , I’m able to select “recognized” text, but when I copy the text to clipboard I’m getting only dots. All the text is copied as dots. No one character.

Is this a common behavior, bug or limitations of the free version?

Chrome latest version, Windows 10.