If you are using the "UploadBrowserPath" and "UploadFilePath" attributes of cf_sebForm, then you can also use "thumbfield" and "thumbfolder" attributes to display a thumbnail of an "image" field.
By using these attributes, cf_sebField will look in the query passed to cf_sebForm and use the value from the column indicated by the "thumbfield" attribute. It will show the file with this name from the "thumbfolder" directory instead of showing the image for the field itself. This will allow you to display a thumbnail of a larger image being stored in this field.
Note that while cf_sebForm will handle uploading an image, an creation of thumbnail images is outside of what cf_sebForm manages (you might look at Manager.cfc for this).