Click on the Flickr photo you want to use.
Place your mouse over the picture and Right Click
Choose Properties
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Highlight and Copy (ctrl+C) the file URL
http://farm2.static.flickr.com/1024/1248805671_ace89be467_m.jpg
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The URL will end with .jpg ~ do not copy the other information at the end of the URL. See what I have highlighted for example.
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Paste (ctrl+V) into html
This code:
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Produces this Flickr Image:
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Add width="250" after the .jpg" to size the image ~ change 250 to any number depending on the size you want.