Unwanted spacing below images

I have a problem when I post images onto my blog, for some reason my particular theme adds spacing below each image by default – so I’m unable to include text directly beneath an image.

For example, on this page
https://www.banksy- prints.com/print/trolleys-trolley-hunters/
(the gap in the URL needs to be removed to view) the gap between an image and text below is the equivalent of around 3 paragraphs, even though it appears as directly underneath when I edit the page.

Do I need to edit the CCS file? Any input appreciated.