Is there a way to check how much of the picture has been loaded, in pixels, from the top?
<p>The heading sums is all. Though, the case is where I have a long (20x2000px) picture as a sprite for thumbnails. It would be nice if I could start showing the sprite only for the thumbnails that already have required-part of the sprite loaded, and show loader in the meantime.</p>

<p>All I need is to know how much of the picture has been loaded in pixels from the top (supposing that it is not progressive). I thought of using file size to estimate that, though that would be very inaccurate.</p>

<p>The main question everyone is having - <em>why to do this at all?</em></p>

<p>There is a page that displays somewhat 100 thumbnails. It would be a nice thing if this page had a sprite of those thumbnails generated in the descending thumbnail order.</p>

<p><img src="http://i.stack.imgur.com/IHoFb.png" alt="enter image description here"></p>

<p>Such page already exists. The screenshot is attached. User can see a gray placeholder while the sprite is being loaded. I want to display the thumbnail only when the required part of the sprite for that thumbnail is already loaded.</p>

<blockquote>
  <p>@Guy Sounds like a theoretical question then... Per your comment on the answer below, if you're loading 10MB 'sprites' you're doing it wrong.</p>
</blockquote>

<p>No, there is nothing wrong about it if this can be achieved. That would reduce the number of calls by 100 every time the page is being called. That is a remarkable speed improvement even if everything is cached.</p>
