Hey, that’s strange, as in functions.php the image sizes created are only the eight following
/* THUMBNAIL SIZES
================================================== */
set_post_thumbnail_size( 220, 150, true);
add_image_size( 'widget-image', 94, 70, true);
add_image_size( 'thumb-square', 250, 250, true);
add_image_size( 'thumb-image', 600, 450, true);
add_image_size( 'thumb-image-twocol', 900, 675, true);
add_image_size( 'thumb-image-onecol', 1800, 1200, true);
add_image_size( 'blog-image', 1280, 9999);
add_image_size( 'full-width-image-gallery', 1280, 720, true);
so the 1024 size for example is not part of the theme’s code. Maybe it’s wordpress’ core image sizes then.
Cheers