Well, the problem it´s, on trinitronic website says this extension is compatible with K2. That suppost to means, work with any image option from K2 component. Images inserted by normal Joomla Editor is not K2 element, it´s Joomla element. So K2 suppost image means that Main Image from each Iten, also, images from K2 gallery.
Resuming: This extension don´t work with K2 Components, also have some issue about JoomSEF, after I enable the Nice WaterMark Plugin, my JoomSEF website stop working.
No images get WATERMARKED, so it´s not true work with K2, also have bugs around SEF.
I know it´s so cheap, but anyway, doesn´t matter how much it´s, that suppost work, and right now don´t!
The right thing to do it´s FIX that and make work with K2 like said above on description. because if some like me paid for, it´s because I need that working.
The above extension listing very clearly states,
"Simply add a tag in an article, custom module or just about anywhere text can be added... ...the Nice Watermark plugin will replace the tag with a watermarked version of your image."
The online documentation also explains the same thing. And during the technical support we provided, we repeatedly explained to you that you needed to enter a tag into your K2 content.
The extension works exactly as it was designed to work. You simply refused to use the plugin as instructed.