Explanation: in libesci-interpreter-gt-f720.so in libesci_interpreter_gt_f720_342::libesci_interpreter_gt_f720_348 at 0xdf74: the binary blob esfw8b.bin is searched either in /usr/share/esci/ or in $ESCI_FIRMWARE_DIR. But since this library is to be used wia libsane.so in every binary in the system, we can't wrapProgram the relevant executables to set this environment variable. Instead, we patch iscan to set this variable before loading libesci-interpreter-gt-f720.so. --- backend/channel-usb.c.orig 2017-08-14 11:24:27.669582456 +0200 +++ backend/channel-usb.c 2017-08-14 11:31:40.509010897 +0200 @@ -169,6 +169,10 @@ { SANE_Status s; + setenv("ESCI_FIRMWARE_DIR", NIX_ESCI_PREFIX, 1); + setenv("ISCAN_FW_DIR", NIX_ESCI_PREFIX, 1); + setenv("ISCAN_FIRMWARE_DIR", NIX_ESCI_PREFIX, 1); + s = sanei_usb_open (self->name, &self->fd); if (SANE_STATUS_GOOD == s)