Comment on WordPress SEO by SEO Dave.
Adding thumbnails to a WordPress theme isn’t an easy thing to do, every archive template file needs the code and it needs to be built into the theme in otherways. The code I use for Stallion 6.2 (and will be added to the next release of Talian) also includes specific code for other Stallion features like the Stallion featured images, so not possible to add it to Talian 3.
If you are set on not upgrading from Talian 3 look to see if there’s any thumbnail plugins as I’m not making any changes to the Talian 3 code (not looked at Talian 3 in years).
You are missing out on loads of features sticking with Talian 3, Talian 5 (40+ options) was a big update and Stallion 6 (250+ options) was a big update from Talian 5.