images on subdomain are not https… ?

Hi, I am using version 3.3.6 of WordPress HTTPS (SSL).

I have a wildcard certificate which, when i load an image directly from a subdomain, perfectly loads in https.

My issue is that i have a https paypal return page. This page loads images from the subdomain, where all images are hosted.

The certificate warns :
Your connection to http://www.pixxler.com is encrypted with 256-bit encryption. However, this page includes other resources which are not secure. These resources can be viewed by others while in transit, and can be modified by an attacker to change the look of the page.

Now i do not know what to change… I tried looking into htacces, but could not find a solution which fits me, because not all pages need to be https…
Could anyone suggest me what i am doing wrong ?

thank you all very much!!

http://wordpress.org/plugins/wordpress-https/