Images going behind https incorrectly

Hi Support, I have approached the authors of my framework/theme and and they have held their hands high and said it isn’t their issue and I cant find a reasoning why the site is getting cached with some images as
https:

I really need to get this sorted as it is causing me issues and I really need to cache the sites to speed them up. If I clear the cache the problem resolves. Could this be a combination of server settings and the caching of pages.

Any advice? if you look at http://www.allkindsofblinds.co.uk/ site you can see some images in the scroller are gone and when I look at the source code they are

EG: In source code <img src=”https://www.allkindsofblinds.co.uk/wp-content/uploads/2014/05/Gloss-Black-e1400518088420.jpg&#8221; class=”ls-bg” alt=”Gloss Black” />

Should be

<img src=”http://www.allkindsofblinds.co.uk/wp-content/uploads/2014/05/Gloss-Black-e1400518088420.jpg&#8221; class=”ls-bg” alt=”Gloss Black” />

Thanks in advance for any suggestions. . .

https://wordpress.org/plugins/w3-total-cache/