force default sizes

Hello,

I am not sure I understand exactly what you need to achieve. By default, any image size that is not generated would be rendered on the pages with the full image size (the original file you upload). This is how WordPress renders the images. There is nothing implemented that can approximate and replace images programmatically based on some type of match. However, depending on the context, you can create advanced rules with my plugin to generate only the image sizes you select.

The way I do in my projects is like this:
– first, I assess the front side and decide from the content which images proportions are similar. Then I make a list of which image sizes can be rendered as the native thumbnail, which as the medium, which as the large and so on.
– then, I adjust the thumbnail/medium/large media settings in order to fit as good as possible the expected sizes
– then I would create the custom rules to generate only these specific images sizes for the custom post types, or pages or posts targeted with categories or tags.

Let me know if this helps.

Regards,
Iulia