Start here:
https://winscp.net/eng/docs/faq_script_modified_files

Here is what my target is
I've used the GUI to upload all the image files to my target site.
Now what I want to do is to only send NEW or updated files to the target site

the ideal execute the vb.net program that would only upload any file added today the source directory, instead of uploading all the files everyday which takes an hour.

Currently I have
'Upload files
Dim MyTransferOptions As New WinSCP.TransferOptions
MyTransferOptions.TransferMode = TransferMode.Binary

Dim transferResult As TransferOperationResult
transferResult = mySession.PutFiles("\\aiken\IDPhotos\*.jpg", "/studentpics/", False, MyTransferOptions)

'Throw on any error
transferResult.Check()

but I'm not sure how to isolate the new files.