treos said:
the source page is "not found" so it can't be replaced with a larger version through this "raw" method.

Not so fast! If you have the direct image link you can update the image even if the source post is gone. For example post #1039922 had the image http://68.media.tumblr.com/820e9d1aa6b4f349b9a09a5de17a4554/tumblr_og3u3kigom1vn7pt5o3_1280.png. The source post (http://the-mary-berry.tumblr.com/post/152718323953) is gone. But change 1280 to raw and you get http://68.media.tumblr.com/820e9d1aa6b4f349b9a09a5de17a4554/tumblr_og3u3kigom1vn7pt5o3_raw.png which is bigger than the old post so I uploaded it as post #1247649.

And don't forget

Lance_Armstrong said:
One tip: If an old source link doesn't work, try changing the subdomain to "68.media"