Here are three image water marking plugins that might full-fill all your image watermarking needs on your WordPress site. All three plugins are developed by the same developers so check them out and and see which works best for you.
If you are looking for a plugin to sell Photos, Images, Digital Print etc in your WordPress site then WordPress Plugin Repository has a brand new plugin which sells photos from your WordPress blog easily, you can increase your photo selling conversion rate with one-click PayPal checkout, you can embed beautiful e-commerce photo gallery and you don’t require any advanced technical knowledge for using this plugin.
Now you can adds a watermark signature or image to all of your uploaded images in your WordPress site. Signature Watermark plugin uses PNG images with transparency for watermarking your site’s images.