Email Signature Manager version 8.x
Email Signature Manager version 7.x
In certain circumstances, for example when Windows font size is configured as 125% or 150% on high resolution displays, Outlook and OWA resize images if the image size if not specified in the HTML signature.
Email Signature Manager 8.4.0 and later, used in combination with Email Signature Manager Agent 3.1.0 and later, automatically sets the image size in the HTML signature and also includes code to ensure the image shows correctly at different Windows font size settings.
If you are using an earlier version you will need to upgrade to resolve the issue.