You can view the extensions which XY includes in each of those File Types by selecting them and then pressing F1 while the control is still focused.
Here a fresh instance of XY v15.90.0020 has:
Image files wrote:*.arw, ARW File, (None)
*.bmp, Bitmap image, Windows Photo Viewer (C:\Program Files (x86)\Windows Photo Viewer\PhotoViewer.dll)
*.cpt, CPT File, (None)
*.cr2, CR2 File, (None)
*.crw, CRW File, (None)
*.cur, Cursor File, Microsoft Visual Studio 2010 (C:\Program Files (x86)\Microsoft Visual Studio 10.0\Common7\IDE\devenv.exe)
*.dcr, DCR File, (None)
*.dib, Bitmap image, Windows Photo Viewer (C:\Program Files (x86)\Windows Photo Viewer\PhotoViewer.dll)
*.dng, DNG File, (None)
*.emf, EMF File, Paint (C:\windows\system32\mspaint.exe)
*.erf, ERF File, (None)
*.fff, FFF File, (None)
*.gif, GIF image, Internet Explorer (C:\Program Files\Internet Explorer\iexplore.exe)
*.ico, Icon, Windows Photo Viewer (C:\Program Files (x86)\Windows Photo Viewer\PhotoViewer.dll)
*.jpe, JPEG image, Windows Photo Viewer (C:\Program Files (x86)\Windows Photo Viewer\PhotoViewer.dll)
*.jpeg, JPEG image, Windows Photo Viewer (C:\Program Files (x86)\Windows Photo Viewer\PhotoViewer.dll)
*.jpg, JPEG image, Windows Photo Viewer (C:\Program Files (x86)\Windows Photo Viewer\PhotoViewer.dll)
*.mef, MEF File, (None)
*.mrw, MRW File, (None)
*.nef, NEF File, (None)
*.nrw, NRW File, (None)
*.orf, ORF File, (None)
*.pef, PEF File, (None)
*.png, PNG image, Windows Photo Viewer (C:\Program Files (x86)\Windows Photo Viewer\PhotoViewer.dll)
*.psb, PSB File, (None)
*.psd, Adobe Photoshop(tm) image, GNU Image Manipulation Program (C:\Program Files\GIMP 2\bin\gimp-2.8.exe)
*.raf, RAF File, (None)
*.raw, RAW File, (None)
*.rle, RLE File, Paint (C:\windows\system32\mspaint.exe)
*.rw2, RW2 File, (None)
*.rwl, RWL File, (None)
*.sr2, SR2 File, (None)
*.srf, Server Response File, Microsoft Visual Studio 2010 (C:\Program Files (x86)\Microsoft Visual Studio 10.0\Common7\IDE\devenv.exe)
*.srw, SRW File, (None)
*.tga, TGA File, (None)
*.tif, TIFF image, Windows Photo Viewer (C:\Program Files (x86)\Windows Photo Viewer\PhotoViewer.dll)
*.tiff, TIFF image, Windows Photo Viewer (C:\Program Files (x86)\Windows Photo Viewer\PhotoViewer.dll)
*.wmf, WMF File, Paint (C:\windows\system32\mspaint.exe)
*.x3f, X3F File, (None)
Photo Files wrote:*.arw, ARW File, (None)
*.cpt, CPT File, (None)
*.cr2, CR2 File, (None)
*.crw, CRW File, (None)
*.dcr, DCR File, (None)
*.dng, DNG File, (None)
*.erf, ERF File, (None)
*.fff, FFF File, (None)
*.jpe, JPEG image, Windows Photo Viewer (C:\Program Files (x86)\Windows Photo Viewer\PhotoViewer.dll)
*.jpeg, JPEG image, Windows Photo Viewer (C:\Program Files (x86)\Windows Photo Viewer\PhotoViewer.dll)
*.jpg, JPEG image, Windows Photo Viewer (C:\Program Files (x86)\Windows Photo Viewer\PhotoViewer.dll)
*.mef, MEF File, (None)
*.mrw, MRW File, (None)
*.nef, NEF File, (None)
*.nrw, NRW File, (None)
*.orf, ORF File, (None)
*.pef, PEF File, (None)
*.psb, PSB File, (None)
*.psd, Adobe Photoshop(tm) image, GNU Image Manipulation Program (C:\Program Files\GIMP 2\bin\gimp-2.8.exe)
*.raf, RAF File, (None)
*.raw, RAW File, (None)
*.rw2, RW2 File, (None)
*.rwl, RWL File, (None)
*.sr2, SR2 File, (None)
*.srf, Server Response File, Microsoft Visual Studio 2010 (C:\Program Files (x86)\Microsoft Visual Studio 10.0\Common7\IDE\devenv.exe)
*.srw, SRW File, (None)
*.tif, TIFF image, Windows Photo Viewer (C:\Program Files (x86)\Windows Photo Viewer\PhotoViewer.dll)
*.tiff, TIFF image, Windows Photo Viewer (C:\Program Files (x86)\Windows Photo Viewer\PhotoViewer.dll)
*.x3f, X3F File, (None)
EDIT: Also the types listed under
Images corresponds to those in the
Image Files category of
Tools > Configuration > Preview > Previewed Formats.