Submit Image Files

I need my clients to submit document scan images for processing. Each batch of these images would be output of an ADF scanner and processed against a request created on website. There would be about 400-600 images (0.3-0.7MB each) per batch and around 10 requests per week. I am not able to figure out how client can submit this data. Different options popped-up like uploading to an FTP and put that FTP path in the request. To use AWS S3 bucket.

I am not able to figure out process flow and options for this. Please share your thoughts on this.