Alex Vita from Foreground Web published a great article on why you should never upload high-resolution images to your photography website. He points out that this is the case for sites that are NOT eCommerce based. You can read that article here.
The case Alex makes is that your website needs smaller images on the front end, visible to site visitors, in order to load fast. But when selling images, you need to sell from a full-size image for the best print quality. We agree!
That's why in NextGEN Gallery and NextGEN Pro there is an option to Backup Originals and Resize on Upload. With these two features turned on, multiple things happen.
You can upload your high-resolution image which is used to sell prints and digital downloads.
NextGEN Pro will only sell products that will produce quality results for that resolution. You can learn more about minimum resolutions here.
These high-resolution images are converted to a backup file and protected on your server. So no one has the ability to access these without your permission.
The only way for someone to download a copy of your original high-resolution image is to sell it as a digital download.
When you sell a print using the lab fulfillment, NextGEN Gallery (Pro) will create the appropriate file at that high resolution (basically a copy) and then send it to the lab.
When you sell a digital download, NextGEN Gallery (Pro) will create a copy at the correct pixels (longest length) which were sold to the customer. It will then provide the digital download to them at that size.
This means that if you use the watermark feature, then you can watermark the images displayed on your website, but sell images without watermarks.
Note: Be sure to have both Backup Originals and Resize on Upload turned on before using watermarks. That way, if you make a mistake you can revert to the original. Learn more about this.
Resizing on Upload
The last thing we want to cover in this documentation piece is the resizing feature. With this turned on at the same time as Backup Originals, a few things happen.
First, as you've read, it will create a smaller version of the image you upload which is displayed on the front end and visible to site visitors.
This is essential to site speed. These resized images can also be compressed using a third-party plugin like Imagify or Shortpixel.
NextGEN Gallery (Pro) will create a retina based version for Pro galleries which offers more clarity and load speeds for non-retina and retina based screens.