I use scanimage in connection with ImageMagick for automated scanning in my ERP systems. Suddenly it broke and convert started complaining:

scanimage [...] | convert - -compress jpeg -quality 100 -density 100 pdf:- > tmp.pdf
convert: not authorized `pdf:-' @ error/constitute.c/WriteImage/1072.

ImageMagick introduced some policies. They need to be adjusted to be able to write PDF as before. https://stackoverflow.com/questions/42928765/convertnot-authorized-aaaa-error-constitute-c-readimage-453#93 worked for me.