Outlook 2013 Signature Image resizing

Hi everyone

I am having an issue with Outlook 2013 whilst amending an email account signature. Essentially, whenever I add an image to the signature file that I am creating or updating, Outlook resizes the image if it is over 600 pixels wide. This of course results in a distorted image when sending an email. When using right-click to display the size and position of the image when it is part of the a new email, it shows a scale percentage of less than 100% (presumably due to the resizing of the image when creating the signature).

I have read other posts and replies that refer to using 96 dpi (which I am), and Windows text display sizes greater than 100% (they are not), but I cannot add any image greater than 600 pixels without it being re-sized.

My second issue is that having created a new signature image, I need to update signatures for multiple users, but replacing/updating  the image file in the 'appdata/roaming..../signatures' folder (even with a <600 pixel width) does not appear to update the image attributes held by the email theme/signature files, and the new image retains the old dimensions, and is distorted.

Is it possible to edit the signature without logging in as each user to use the 'Signature GUI' within the Outlook options/mail settings?