Don't scale a certain image

Most of the time custom theme images (like headers) will apply the dimensions you configure on the Imsanity settings page under “Images uploaded elsewhere” There is no guarantee this is true unfortunately because themes can do whatever they want – including handling their own uploads. But, generally if they follow the recommended practices then they will utilize the built-in WordPress upload functionality – in which case Imsanity settings for “Elsewhere” will kick in.

So, what you can do is leave the Imsanity Page/Post and Media Library dimensions as they are, but change the “Elsewhere” dimensions to something really large like 5000×5000. That way those “other” images will not get reduced.

Thanks! It works!