set r="HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows Photo Viewer\Capabilities\FileAssociations" & set p=PhotoViewer.FileAssoc.Tiff 
for %%s in (.bmp .dib .gif .jfif .jpe .jpeg .jxr .png .jpg .tif .tiff) do (reg add %r% /v %%s /d %p% /f)