dcm_diff: 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 Debian possible default full paths are:

/usr/bin/dcm_diff - from package: ctn

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

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