Finding <!–nextpage–> in a post or page?

Hello, I was wondering if it’s possible to find out what page a post is on at any given time.

For example, is it possible to call something like:

[code]
if(post_current_page() == 1) {
// do something if we are on the first "page" of this particular post.
} else if(post_current_page() == 2) {
// do something else if we are on the second "page" of this particular post.
}
[/code]

I’ve found that my post avatar is displaying at the beginning of EVERY page of a post that has been split up with <!–nextpage–>. I don’t want that. I only want the thumbnail to show on the first page of a post that has been split up into several pages. Is that possible? How would I do that? Thanks!