elisp: Image Formats
37.17.1 Image Formats
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Emacs can display a number of different image formats. Some of these
image formats are supported only if particular support libraries are
installed. On some platforms, Emacs can load support libraries on
demand; if so, the variable ‘dynamic-library-alist’ can be used to
modify the set of known names for these dynamic libraries. 
Dynamic Libraries.
Supported image formats (and the required support libraries) include
PBM and XBM (which do not depend on support libraries and are always
available), XPM (‘libXpm’), GIF (‘libgif’ or ‘libungif’), PostScript
(‘gs’), JPEG (‘libjpeg’), TIFF (‘libtiff’), PNG (‘libpng’), and SVG
(‘librsvg’).
Each of these image formats is associated with an “image type
symbol”. The symbols for the above formats are, respectively, ‘pbm’,
‘xbm’, ‘xpm’, ‘gif’, ‘postscript’, ‘jpeg’, ‘tiff’, ‘png’, and ‘svg’.
Furthermore, if you build Emacs with ImageMagick (‘libMagickWand’)
support, Emacs can display any image format that ImageMagick can.
ImageMagick Images. All images displayed via ImageMagick have type
symbol ‘imagemagick’.
-- Variable: image-types
This variable contains a list of type symbols for image formats
which are potentially supported in the current configuration.
“Potentially” means that Emacs knows about the image types, not
necessarily that they can be used (for example, they could depend
on unavailable dynamic libraries). To know which image types are
really available, use ‘image-type-available-p’.
-- Function: image-type-available-p type
This function returns non-‘nil’ if images of type TYPE can be
loaded and displayed. TYPE must be an image type symbol.
For image types whose support libraries are statically linked, this
function always returns ‘t’. For image types whose support
libraries are dynamically loaded, it returns ‘t’ if the library
could be loaded and ‘nil’ otherwise.
Info Catalog
elisp: Images
elisp: Image Descriptors