No graphicsmagick command line callings seem to work correctly. For example:
william@william-solus ~/Documents/Test/gm $ gm convert Lenna.png Output.jpg gm convert: No decode delegate for this image format (Lenna.png).
Compiling an updated (1.3.26) version does not yield any differences (though does resolve the currently patched CVEs).
Curiously, the program seems to think it has support for these features.
$ gm version GraphicsMagick 1.3.25 2016-09-05 Q16 http://www.GraphicsMagick.org/ Copyright (C) 2002-2016 GraphicsMagick Group. Additional copyrights and licenses apply to this software. See http://www.GraphicsMagick.org/www/Copyright.html for details. Feature Support: Native Thread Safe yes Large Files (> 32 bit) yes Large Memory (> 32 bit) yes BZIP yes DPS no FlashPix no FreeType yes Ghostscript (Library) no JBIG no JPEG-2000 no JPEG yes Little CMS yes Loadable Modules yes OpenMP yes (201511) PNG yes TIFF yes TRIO no UMEM no WebP yes WMF no X11 yes XML yes ZLIB yes [...]
This issue likely slipped through the cracks due to testing using convert and identify, rather than gm convert and gm identify, which resulted in ImageMagick binaries being used.