Twenty Sixteen Pictures help

I like the twenty Sixteen theme, it is clean and simple, but I have ONE problem!

My pictures are the same size and width as the text, while in the preview of the theme pictures are wider with overflows to the left.

Anyone knows why this isn’t happening with my pictures?
I want them to overhang the column, but it doesn’t happen and I don’t think I’ve done anything else than uploading the pictures.. and they are over 840px.