This plugin is a good idea. However, I installed it for a client, and was very much surprised to see - when I was inserting an image to her post - that there were options as to where to place the watermark, what size to make it, and what size images to apply it to. (I was surprised because I thought these options were not possible unless you obtained the paid-for version.) When I attempted to use these settings (because they were there, and available), I was given 1) a popup window that indicated these options were only available for the paid-for version, and when I closed the window 2) I was taken to the developer's website, and told about the benefits of upgrading.
Now, I understand wanting people to upgrade. But you should not have the options showing up there, ready to use and confusing the end user, and then when they try to use them, you're taken away from their site while they are trying to write a post. Granted, it's open in a new window, but still. It's jarring (and the message in the popup immediately made me think I had some kind of virus). And if you're "in the flow" of writing, it causes you to break your concentration, etc. I.e it p****es people off to be forced to do something they weren't expecting. I *knew* such options weren't available to me when I obtained the free version, but to have them show up anyway is confusing and annoying, and then to be taken somewhere I wasn't expecting AT ALL added to that confusion and annoyance.
On top of that, after I got over the initial surprise at these actions (not something I think your average Joe would do, because I'm a developer, and I'm always looking for good resources), I read about the benefits of upgrading, and went to actually purchase it. I can see this being useful for clients. However, 1) I was REQUIRED to join the site; 2) I could not find a single PayPal option to pay with (doesn't mean it wasn't there - I just could not find it); and 3) I was REQUIRED to divulge information I was not ready to do (i.e. name, phone number, address, etc.)
No purchase by me. I don't like being forced to go to someone's site, and then being forced to "join up/create an account" to purchase something, nor do I like being forced to divulge information to purchase something (with PayPal, I don't have to divulge anything save my email address - with someone I've never done business with before, this is my preference).
I gave this plugin 2 stars just for these issues alone. I never actually got a chance to see if it actually works or not - so I didn't indicate that it worked for me or not - all I can say is that it doesn't if you already have images uploaded in your Media Library. My watermark didn't show up on existing images at all. I didn't take it any further.
Do not take this as an "angry vent" type post. It is not. I could have left my rating as-is and never said anything more. But I did feel it might be beneficial to tell the developers WHY I gave it a poor rating, in hopes of helping them out. *Tricking* people to go to your upgrade page with no choice (yes, it *is* a trick - there's no bones about that) leaves an "underhanded car salesman" taste in the end-user's mouth. Instant distrust. Then you require someone to join your site AND require personal information from someone who's already inclined to distrust you? I'd imagine in your stats you're showing a lot of abandoned carts. This would be why.
Hopefully you'll rethink your process here. I already knew that I wouldn't get a lot of goodies because I was using the free version. If the free version worked well, I would have, indeed, gone to the site to review benefits of upgrading. And if PayPal had been available, I would have instantly purchased the plugin. But this process? No way. I'll find something else.
http://wordpress.org/extend/plugins/transparent-image-watermark-plugin/