Whenever you upload assets into Dash, Dash will compare the assets to other assets in your upload and assets that already exist in your Dash account.
Once the duplicate detection is complete, you will have the opportunity to remove the duplicates from the upload before you submit the rest of your assets into Dash.
Currently, we only consider an asset to be a duplicate if it is an identical file (based on an MD5 hash). This means that the entire contents of the file must be identical. The filename is not considered part of the check.