Something to be aware of is that email attachments are scanned by your ISP's mail system on upload, this slows the upload down significantly, also a lot of AV programs scan attachments on the way out and the combination of the two, on a large file, screws things up totally, so try turning the 'scan e-mails on sending' option off in your AV program. You can scan the picture prior to attaching it as a totally separate operation if you wish.
(At least that's how it worked a few years ago I presume it's still the same)