pnmhisteq: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/bin/pnmhisteq - from package: netpbm-progs

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/pnmhisteq - from package: netpbm

You may install the required package with command apt-get install {package}

Error in other languages:
pnmhisteq: bevel nie gevind nie
pnmhisteq: comandă negăsită
pnmhisteq: comando não encontrado
pnmhisteq: commande introuvable
pnmhisteq: command not found
pnmhisteq: käsku ei ole
pnmhisteq: không tìm thấy lệnh
pnmhisteq: komanda nerasta
pnmhisteq: Kommando nicht gefunden.
pnmhisteq: kommandot finns inte
pnmhisteq: komut yok
pnmhisteq: nie znaleziono polecenia
pnmhisteq: níor aimsíodh an t-ordú
pnmhisteq: no se encontró la orden
pnmhisteq: no s'ha trobat l'ordre
pnmhisteq: opdracht niet gevonden
pnmhisteq: parancs nem található
pnmhisteq: perintah tidak ditemukan
pnmhisteq: príkaz nenájdený
pnmhisteq: příkaz nenalezen
pnmhisteq: команда не найдена
pnmhisteq: командата не е открита
pnmhisteq: 命令找不到
pnmhisteq: コマンドが見つかりません