How CryptoPHP: Sneaky malware works?

This malware is hidden in pirated themes and plug-ins for CMS . the ‘social.png’ file confirmed we had found the backdoor; as it contained a big blob of obfuscated PHP code .

My question is how hacker use the code infused inside an image ?

Can i execute an image file as a php keeping php code in an image ?

Even if i infuse some php code in a binary or hexa format into an image file , how hackers use the image .

How to use the code infused inside an image .