There's not a way to attach photos, but you can add images if you use a third-party photo-sharing program like Picasa or Flickr.
These websites generate a code for your image that you can embed in your email templates. Copy the code from your photo-sharing site and go to your Full Slate account under Messages > Templates. Choose the template you want and add something like "PHOTO" where you want the picture to be placed. Then, on the toolbar above the body of the email, go to HTML mode by clicking the right-most button that says 'Edit Source' when you run your mouse over it. Find the word you added ("PHOTO") and paste the unique link over the top of it.
When you switch back to regular mode (by again clicking the Edit Source button), you should see the picture there.
If you're using Flickr, here are the specific steps to obtain your photo's embed code:
- Open up the photo in your Flickr account.
- Click the 'share' icon in the lower-right part of the screen (it looks like a rectangle with an arrow coming out of it).
- Select "Grab the HTML/BBCode" and then click the "HTML" radio button (rather than "Embed" or "BBCode").
- Copy the resulting code to paste into your Full Slate template per the instructions above.