In Mail, why does the logo in my signature appear so big?

I've set up a signature in Mail that includes a jpg of my company logo. In the signature and in my outgoing emails it is the size I want it (ie a few cms) but in the recipient's email it expands to about 15 cms. How do I make it stay the same size?

And while writing about signatures, I have 3 (2 different companies and home); all have a short name. In the "Choose signature" field 2 show under that name, one shows all of the content in the sig. Why? How to get them all to show as the short name?

Thanks

Ian