Hi!
Thank you for your response!
Yes, I installed one new plugin. Going to delete it now as it is not important to my page yet.
And yes everything is still in my wp-content folder. What is weird is that I see ? marks instead of the picture in the WordPress media area, but when I click on the ? marks, it still opens my pictures.
Hope deleting the plugin will help, otherwise I will come back here :).
Best regards!