Auto Image Resizer

I’m building this external application that is going to upload new posts into the DB automatically. I have everything working except the image portion. When you add an image/gallery to a post through the dashboard, it automatically creates multiple versions of the image, all of different resolutions (e.g. pic.jpg, pic-90×90.jpg, pic-300×200.jpg, etc.) as they’re set in the media settings.

My question is, is there a way for me to upload one file externally, and then have WP recognize it and create all the different sized versions? i.e. I have my application drop an image into the “autoResize” directory and it creates all the new versions?