Stop blog image opening as a full screen image

Hi – our blog post images open as a full screen image with a grey background, you either have to hit the back arrow in the top menu bar or if you hit the ‘x’ the whole page closes. In the parabola demo blog images open in the same window just a bit larger with a white box around them, I assumed that was the default setting, what do I have to do to make that happen?
thanks.