The best size and format for adding a logo is:

Image Types

.gif is the default image type and all other image types loaded will be converted to .gif
.jpg, .tiff & .png are the other supported image types.

For the best result use a properly sized .gif file so that no image processing occurs.

The optimun image size is 140H x 400W to place the logo so that the address section will appear in window faced envelopes.

The maximum image size should be 800H x 600W for no processing to occur. An images this size will push other fields so that the address fields will not appear in the window envelope section.

Please click on this link that will take you straight to the HELP file for adding logos -