TV Channel Logos are stored (default) at User>UserName>Appdata>Roaming>J River>Media Center 21>Files
My suggestion is for future MC versions to rename folder "File" to "Logos" to make it easy for Users to figure out where their TV Logos are stored, and to be consistent with the other folder "naming conventions" such as "Albums", "Artists", "Seasons", "Series" (where the folder names describe the folder's contents).
Obviously a very minor detail, but possibly helpful to those users trying to figure how the program works (and who may want to work within, or backup, the "TV Logo" folder).