I have scanned most of my old photos. Most are TIFF format and generally around 10-12 Mb in size. As these are pre-digital camera photos the  'date taken' actually reflects the scanning date; rather than the actual 'date taken'. I am trying to make the change in Windows Live Photo Gallery. Changing the scanning date to reflect the actual date taken is not the problem. The problem is that in making the change Windows arbitrarily not only changes the file format to JPEG but also (significantly) reduces the file size. I would like to be in control of what format and file sizes I want without being over ruled by Windows. Appreciate any advice on how to change the scanned 'date taken' to reflect the actual 'date taken' and retain my file format/file sizes.

Much appreciated