[Plugin: NextGEN Gallery] Is the "Set Watermark" a permanent part of the image?

Can someone tell me how the “set water mark” works? Does it make a new copy of the image so the old one doesn’t get marked?

I’d like to keep a “clean” digital image of these images (that is one without a watermark).

I’m working with little old ladies at a historical society and I’m concerned they will “forget” to make a backup when they upload them.

Literally, they are keeping their photos in an old version of Microsoft outlook on a 10,000 year old computer that is not backed up. The Nextgen interface seems very simple for them to use and I’m hoping they will, instead put their scanned in photos into the wordpress database where, at least it will get backed up.

They were afraid people might steal the images if they didn’t have a watermark…a legitimate concern, but I need to keep a clean copy.

Will the plugin automatically keep a clean copy? Or will it permanently alter the image if I use the watermark feature?