My fix for this is to start off with small versions of the pictures, e.g. 800x600, which Flickr etc will readily do.
But if you insist on starting off with something huge the fix is to edit the HTML for the picture insertion and add width="95%". This makes the picture take up 95% of the width of the reader's blog page. It does NOT do anything about file size, loading speed or bandwidth, however, which is why using smaller pictures is a better fix. Or do both, of course!
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