Make Google Index Full Sized Images

Hello everyone! This issue has been baffling me for years and I haven’t found a proper resolution yet. Basically, I want google to index the full-sized images instead of resized images. For example, I upload a 1000*800 resolution image for a blog post and then change it to medium size (300*300) so that it doesn’t weigh down the page. But when I do so, I notice that google indexes the medium size (300*300) image instead of full sized image. Is there any way to make google index the full sized image? I’ve noticed several wordpress users do that. Thanks in advance?