Finally got this plugin to work the way I wanted ….
On one client site, we have a mixture of pictures, some we want watermarked, some we do not.
Install and Activate Easy Watermark.
FLUSH THE BROWSER CACHE!
Go to Easy Watermark Settings -> General. Uncheck anything that will automatically apply the watermark (‘Auto Watermark’, ‘Allow to Auto Watermark’, and all the Post Types.
NOTE: it would not let me deselect all the post types, so I selected a post type we don’t use (FAQ) and deselected the rest.
DECISION TIME – you can remove the watermark later if you check the ‘Backup – Save original images …’ box. This will create another copy of your images, so decide if you have enough storage space for this option. If you don’t, save the originals on your computer somewhere outside WordPress.
Select all the Image sizes (otherwise, a right-click on the thumbnail will let them download an unmarked version of the large image.) Save Changes.
Go to Image tab. (if you’re using an image watermark) Upload the watermark image file (or get it from the Media Library if you already uploaded it) and make positioning settings. Save Changes.
Now the watermark should not be applied when you upload images.
Go to the Media Library, and a new option should appear called ‘Add Watermark.’
You can go down the list and add the watermark to select images.