Difficulties with a picture in a signature

I have made a signature with a picture (png) in it: picture left, text right in a table with one row and two cells (the only way to place a picture and text on the same ‘line’).

But: I hear from people who recieve the mail the picture is out of proportion: much bigger than the text while in the original I made the two match perfect.

How can I make sure that this does not happen: fixed sizes for text/picture in the same widht and hight?