Ignore specific sizes

Hello,

On my website, I have a plugin that handle custom avatars. When a user add a new photo as an avatar, two custom sizes are generated (32 x 32 and 64 x 64). When I add an image somewhere else on the website, since it’s not usefull for me to have 32 x 32 and 64 x 64 images generated each time, I haven’t added add_image_size() for this.

The problem for me is that when I regenerate thumbnails with your plugin (which is awesome btw), the images 32 x 32 and 64 x 64 are deleted, because I like to clean the whole folder.

My question : is it possible to specify to the plugin to ignore images generated with a specific size, in my example 32 x 32 and 64 x 64 ?

Thank you 🙂