Is https required for image tracking?

I have a site that doesn't run any java, so I have been using the Piwik image tracking option. However, Piwik tells me I have to use https in the image location code, but I know that this causes various warnings on various browsers and devices - IE will report that not everything on the page is secure and won't load non-secure parts of the site, giving users an empty page, plus not every browser and device accepts StartSSL certificates, bringing the dreaded 'untrusted certificate' warning.

Can I just replace https with http in the address for the image code and have it otherwise work the same?