jpg to tns conversion is usually related to the transfer (or at least attempt) of JPEG pictures to TI-Nspire series of graphing calculators developed by Texas Instruments. This is of course doable, but possibly only certain pixel sizes of the pictures can be transferred, so you may need to resize the file first to the proper size.
You can also find dedicated utilities provided by TI that allow users to transfer texts, pictures and other documents to your calculator devices. You may also find small utilities on fan Nspire sites. These usually offer various ways of transferring files to the calculators.Open JPG file Open TNS file