My website is in greek language so i do not if that matters. Whenever i like something through the included plugin maybe it takes wrong picture or even translates the greek characters in english language.
Do you have any idea where the problem is?

Hi. Facebook makes use of the Open Graph meta tags to find information about the content. These tags are not included in K2. You should find a plugin doing this or add them by your own in your template overrides. The second option requires programming knowledge.