I want upload image after resizing on Browser with angular js

I got resized image on browser canvas by javascript.
And I can upload my image to AWS S3 directly from browser.

But the uploaded file is not an image, and I can't see it what I could on browser before uploading.

In process of resizing, I Use 'canvas.toDataURL();' and I put it to target img element's src.
The value of src is 'data:image/png;base64,iVBOR....'.
I think this value should be changed before uploading.

How can I convert it to proper format?