If you use Flickr here are the instructions for linking to a photo that I found and used:
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How do I get the URL of a photo?
To use the URL of a photo (like when you add a photo to your Blogger profile), you must provide the web address (URL) of the image itself, not the address of the web page where the image is displayed.
Here's an example of a correct URL for a photo. Note the .jpg at the end:
»
http://www.flickr.com/photos/132375_0ca82ae31e.jpg
Here's an example of an incorrect URL for a photo. It points
to the web page where the image is displayed, not the image file itself. Notice there's no .jpg at the end.
»
http://www.flickr.com/photos/eric/132375/
(Click both of these links
to see the difference.)
To get the URL of the actual image file, find the photo you want to use. Click the "All Sizes" button above it and select the size you want. If the photo is yours, two text fields appear below the photo. The first contains a snippet of HTML that will produce the photo on your web site, with a link back to the photo page on Flickr. The second contains the URL of the image itself. Simply copy and paste the one you want into your web site.
If the photo isn't yours, you may not be able
to access the Different Sizes page (if the owner doesn't allow downloads of the photo).
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I did a Help Search for "Linking to Photos" to find the instructions. Please note that you can resize the photo for posting in the same step...