Is there a widget for Opera that performs a similar function to firefox's Remove It Permanently (it can remove just about any elemnt of a page, picture or not)?
Add this button: http://operawiki.info/PowerButtons#kill
It highlights in red elements of the page when you hover them. Clicking, pressing enter or pressing space removes the element and goes back into normal mode. Pressing escape goes back into normal mode.
The following pages have a lot of useful buttons. There are also several online button creators that allow you to make your own button with icons/actions/labels easily if you are not comfortable editing .ini files manually.
Opera has a "block content", accessible by right mouse button on the page.
More details on Opera Help.
Though it works for images and active content, but not for text, for example.
Edit For precisely the HTML elements, I don't really know, I don't think there is such thing. In other things that could be useful, you could choose style for a site, change the appearance of it, with the Opera Style Menu