Never upload sensitive documents or personal photos to unknown "free" sites without checking their privacy policy. Beware of "PFX" Scams:

Since a PFX file requires encryption keys, you need a tool that generates those keys and wraps them around your image data (or links the image to the certificate).

Technically, you cannot "convert" pixels into a digital cryptographic key. However, the term "JPG to PFX converter" usually refers to one of two scenarios: