Question About Bulk Upload From Ftp And Replacing Image With The Same Name

If I check this box, does the original file get overwritten and therefore not part of the total count.  As I am uploading the exact same files Because I forgot to click watermark, I am noting the total number of files on the site is continuing to climb.  I thoughit would overwrite it so the numbers wouldnt change.  

Also Is there a better way to add watermarks after the fact, because. I am a dummy

Does it look like the photos actually were overwritten? With that selected, it will just replace the current photo (UPDATE) so the total number of images should not go up.

The watermark is only applied during the upload.