I know, English is hard. It’s ok that you’re wrong, or to put it nicely, confidently incorrect.
JPEG lacks the ph (eff) sound because, well you know, there is no ‘h’ in JPEG and that changes the pronunciation rules. based on your argument, we’d also pronounce picture as ficture. Or penis as fenis.
So, a+ for effort, but F for accuracy.
Fun tidbit though. Person, penis, and peg, all follow different pronunciation rules because the consonants that follow.