Can you specify image sizes in dynamic themes?

Hi there

I’ve been trying to improve the load times of a dynamic site I’m working on and as such have been looking at https://www.gtmetrix.com to see which areas can be improved upon. There were a few things the site got an “F” for and one of these was Specify Image Dimensions – the report stated that 0 images had their dimensions specified.

One of the first things I discovered was that I was unable to specify the images for dimensions, but I could see what the image dimensions were in the media library. I’ve looked through various screens and don’t seem to have an option to state image dimensions; however, I can scale an image and add the width & height dimensions in the social settings of the All in One SEO plugin.

I’ve spent a decent amount of time trying to locate how I can specify image and height dimensions. Am I write in guessing that as the theme is dynamic I shouldn’t be messing that anyway?

FYI I’m running the Hazel theme.

Thanks for your help