Lets face it - sometimes life comes to a point where you need to hand over the reigns of your blog to someone else. You've built a great site, with lots of great content and followers and you don't want to see it die, so you want to bring a new "owner" in to the site and transfer the entire site to them. The process is easy, but unfortunately most people only do 1/2 of the job; they forget to transfer the photos!
You created your Blogger site using a Gmail address, so your Blogger website is tied to that Gmail account. Each and every time that you publish a blog post with images, those images are being stored in a Picasa album that is also tied to that Gmail address. And if you've invited other authors and administrators to your blog, each of them also will have a Picasa album tied to their individual Gmail accounts for the images they've published through your Blog.
If they delete images in those Picasa albums that are being used in your blog they will then show up as big black "missing images" in your blog posts.
And if you are no longer affiliated with the blog, you'd likely want to get rid of the images in your Picasa account that are taking up space (counting against your free space or costing you hosting monies).
You might have noticed in the notes at the end of the ownership transfer step it says "Photos uploaded with Account 1 will break if that account is deleted. If you want your old photos to display after adding Account 2, you'll have to leave Account 1 active." Those instructions are missing the part where they show you how to transfer those images to the new blog administrator so that the old administrator or contributor isn't left storing images for a site they're no longer affiliated with.
Once you've followed the ownership transfer process for your Blogger site, follow this next set of instructions for transferring the images associated with that blog to the new administrator.
We also recommend this being done whenever you have a blog contributor who will no longer be contributing to your blog so that they don't "accidentally" delete the album from their Picasa account and cause images breaks in your blog.