All you do is take your thumbs, do one of them to create an action in Photoshop. The rest of the thumbs will follow that action. It's the same thing as running them through a bulk processor. Photoshop does an excellent job and there is no need to install, set-up, and monkey with additional software.
Depending on the quality you want with your thumbs, the best way to do them is manually no matter what tool you use.
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