Everest
Mechanic
I don't think removing the lock would be too bad of an idea. Isn't it possible to just detect if the thing the text points to is an image or not? Like, if it can create an icon to display, then it's valid. Although with my basic knowledge of programming in general, I'm guessing that would be quite advanced.
Honestly, I could do that, but I'd also have to implement something to check if there are new entries in the input. Even then, any option where you can avoid using bandwidth is better. If it comes to it, I will do that. As is, checking for a valid url seems easier above all.