In most cases, nco to jpg conversion seems to be mainly sought by users that try to recover old JPEG photos (.jpg, .jpeg) from .nco backups originally made using Nero BackItUp tool. The only way to recover these backups is to use the exact same version of the program in which they were made, newer versions won't help you here.
The only workaround this would be to rename nco to zip and extract the content. You will find your pictures there, each in a separate folder, however with renamed file name. You will need to rename all pictures back to their original name (it's how the folder is named).Open NCO file Open JPG file