Hello, waleed;
you are the one who says if any category or image is or not private, in your Admin Control Panel.
If you need that your images will all be public, you have to do nothing. They will be public by default.
Some other features, like votes, uploads, and comments, can be changed in the Admin Control Panel. You can also there bypass the CAPTCHA security (even if it is a sensible point, related to spam bots).
You may just need to have a public website, with no registration. So, you will have to look at your template's files, and erase this:
{lang_registered_user}
and
{user_box}
in any HTML file.
Feel free to ask any help. You'll be welcome.