classifier_tester: 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/classifier_tester - from package: tesseract-ocr

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

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