If the file won't open, open it in a (like HxD). A valid JPG file always starts with FF D8 FF in hex code. If you see those characters, change the file extension to .jpg .
Do not simply rename a corrupted file. First, try opening it in (yes, VLC can open many image formats). If VLC displays the image, then you know the data is healthy; you can then use VLC's "Convert/Save" feature to output a proper full.jpg file. filedot ams jpg full