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.
See Dynamically Loaded 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), JPEG (libjpeg), TIFF (libtiff), PNG
(libpng), SVG (librsvg), and WebP (libwebp).
Each of these image formats is associated with an image type
symbol. The symbols for the above formats are, respectively,
pbm, xbm, xpm, gif, jpeg,
tiff, png, svg, and webp.
On some platforms, the built-in image support that doesn’t require any optional libraries includes BMP images.31
Furthermore, if you build Emacs with ImageMagick
(libMagickWand) support, Emacs can display any image format
that ImageMagick can. See ImageMagick Images. All images
displayed via ImageMagick have type symbol imagemagick.
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.
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.