If you Control click on the photos you can select Display as Icon. But that only affects your email client and not the recipient's. If the recipient's email client is set to not display photos the photos will show as icons. You don't have control over their client.
The only way to have the photos not be displayed is to export them out of iPhoto and zip/compress them by Control-clicking and selecting the "Compress ..." option.
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The recipient will then download and unzip the file to get the photo files.
Happy Holidays