We're thinking of adding key highlights of the product on the top of an overlay of the product image, most probably on the second image of the carousel. I just wanted to understand whether it will be good idea or not. As according to most of the users, product images are the first thing they see when they land on the product page for the first time, giving user the ease to find key highlights on the images itself could help in positive conversions.
Instead of overlaying the highlights over the product image, why not display them right next to it? I understand that they need to stand out and you can do that using design principles like contrast or spacing right next to the product. Users will see them. It is more likely they will see the highlights when they are displayed on the main page rather than if they are hidden on a secondary page in a carousel. Hope this helps!
It's recommended to add descriptions to product images to highlight features and details that might not be obvious by just looking at an image, or will be hard to understand if you only put the features in the product descriptions.
Baymard Institute has performed usability studies that show that it's helpful for e-commerce visitors. https://baymard.com/blog/product-images-descriptive-text
Out of sight – Out of mind If you only put the product features on the second image in the carousel there is a risk that visitors will not discover the text.
This article describes the risk of hiding important stuff in general. https://www.nngroup.com/articles/content-chrome-ratio/
And this article, again by Baymard describes what happens if you put content inside tabs. https://baymard.com/blog/avoid-horizontal-tabs