That's an interesting question.
Actually it seems like it might be several questions.
Let's take them one by one:
Can you have Screenshot Captor take an image every X minutes: yes.
Can you have Screenshot Captor take images while it stays hidden out of the way: yes.
Can you have Screenshot Captor automatically upload every image it takes using an external tool like ZUploader: yes.
Can ZUploader be told to overwrite the new uploaded file with same name as previous upload: i'm not sure, please check and tell us.
Can you have Screenshot Captor be taking these automatic captures of a specific window: not explicitly
You are the first person who has actually ask for this, it's not a bad idea, though it's a bit awkward. You can have SC take a screenshot of active window, but then when you switch away to another window the automatic capturing will start capturing the newly selected window. And if you do a repeat-region capture that will have problems if the window in question is off-screen.
Now, it seems to me that your best bet might actually be not to use Screenshot Captor, but to use it's little brother tool, the commandline based MiniCap
. You could invoke MiniCap from another tool every so often and pass it commandline options to take a screenshot of a specific window by window id or name, save it as a specific name, and then invoke your uploader or ftp tool on that file.
Now I *think* that will work even if the target window is minimized/offscreen but i'm not 100% sure, so you'd have to test that. If it doesn't let me know, because there may be a capture method that CAN, even if im not using it by default -- and I'd be willing to add that to MiniCap.
In summary, try investigating SC and MiniCap and let me know how far you get, and maybe we can try to get you the last bit of the way there once we know what the problems are.