I'm sure there is an easier way to do it but I put selected photos into a file in I-photo,click edit, select all, click "share", click "email" then pick the size ( medium works). From the email I click and drag them onto a file I have on my desktop for car stuff for example and then I get rid of the email. This way pics are the right size. The pics can now go directly into manage attachments. It sounds like a lot but it's actually pretty simple.
