I have been using Kim Klassen's wonderful instructions to use the mouse-over technique, but I have been wanting to use my Flickr Photos instead of having to store my pictures on a different account in order to have a URL to use in the mouse-over code. It is not obvious where to grab the URL from your Flickr photo page but I finally figured it out and I wanted to share it with you here in case you've been struggling with the same dilemma.
First Open your picture and select the "Share" pull-down menu above your picture, then select the "Grab the HTML/BBC Code" menu item. Select the "HTML" radial button below the code box, and select the size of the image that will work for your blog. In my example below, I had already uploaded a re-sized image for my blog, so I selected the "Original" size. Once you do this, you can click in the box with the code and copy it.
You can paste this code as-is if you just want to display the picture on your blog. This code will link back to your picture on your Flickr Photostream if the user clicks on your picture.
If you just want to grab the URL link for your Flickr picture, copy the highlighted excerpt from your code as shown below in my example. This is the URL you would use to paste in your mouse-over code.
If you want to get the code to display this picture on your blog without linking back to your Flickr site, copy the highlighted excerpt from your code as shown below in my example:
Finally, I also discovered that Flickr provides a feature where you can create a blog post directly from your Flickr Photo page for some common blog sites. Simply open your Flickr Photo page, select the "Share" pull-down above your picture. Next, select the "More ways to share" pull-down and if your blog icon is in there select it as shown in example below. It will pop up a window where you can create your blog entry.
I hope this helps! Have a great day! :-)