In our system watermark can be kept only by overwriting .png files. You need to create a transparent .png file and overwrite that filecomponentscom_odudecardincludewatermark.png Do enable watermark from ODude Ecard Setting page
Changing thumbnail can be set at ODude Ecard Setting page. There is only width and no height at settings. It will try to adjust the maximum width of the image and same in a ratio the height will be adjusted.