This indicates an attack attempt to exploit a Command Injection Vulnerability in YouPHPTube Encoder.
A remote, unauthenticated attacker could exploit this vulnerability by sending a crafted request to getImageMP4.php. Successful exploitation could result in arbitrary system command execution under the context of the server process.
YouPHPTube Encoder 2.3 prior to commit 688b19445f28209ad727d0aeab5b47d819a6c7b4
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.