why would a photo cause gibberish in email?

[mrbigstuff]

You're using the web interface for Gmail?
Yes
Is the file named properly with .jpg at the end?
Yes
Has the recipient forwarded the message back to you so that you can check it out for yourself?
Yes
Have you tried resending the original message with one of your other email accounts as the recipient so you can see if it's really Gmail at fault?
No, will try
When you look at the sent message in your sent mail box, does the image appear to be attached properly there?
Yes

I will add that this is the first time I've had this happen in many a year.