Hi @alex_nicholas,
I can't say anything about the error itself but the PHP version shouldn't be the problem.
But, also, you're Magento version is really old and you should be ready to move forward with version upgrade.
At least you can try to move to the latest Magento 1.9.x to be able to get support for PHP 7.2 (since PHP 5.x will lose any kind of support next month).
(my 2 cents)
If you look at the source with "fetch with Google", rather than looking at the render does it show all image code, along with their alt attributes etc ? if so consider it a rendering bug IMO.
As a fall back though you could wrap your images in <noscript> tags to get around the rendering issue but if it's showing in the source I wouldn't worry about it too much.
The upgrade should be fairly straightforward. i wouldn't do it in a live environment though. Setup a dev area (potentially on a subdomain) and do the upgrade there. You most likely will have installed modules that could potentially break on a newer version so doing this on a dev will highlight those.