You can set thumbnails parameters byc changing the values of the parameters:
Thumbnails.Url = BaseUrl + "_thumbs/"; Thumbnails.Dir = ""; Thumbnails.Enabled = true; Thumbnails.MaxWidth = 100; Thumbnails.MaxHeight = 100; Thumbnails.Quality = 80;
Url and Dir
The Url and Dir properties defined the folder used to hold all thumbnail images, and the URL to access them. It works just like the BaseUrl and BaseDir settings.
Enabled
By setting Enabled to "false", CKFinder will have no support for thumbnails.