I am scanning photos and saving them as a tiff file. The MAC OS does not add the file extension. How can I force the file to be saved with the proper file extension? My Windows PC on the network does not recognize the file type until I add the extension on the file.

Thanks

Are you sure the file extension is no saved? Maybe it is just not shown to you? Are you sure your Windows PC recognises both the .TIF and .TIFF variations?

in the program used to SAVE the image,
be sure to set the image type (tiff, jpg, gif, png)
and then just manually add the proper extension to the name.

OS 9 does not add extensions, as Mac does not use that technique to recognise the encoding.

OS X can be config'd to add PC compatible extensions for you

btw; if you know for sure how it was saved, then just RENAME the file
on the Mac or the PC.