I remember trying to explain that checking the file extension of a file doesn't mean that it is actually an "image" file. I was an intern at my first internship, but wasn't taken seriously when I proposed [to the senior dev] that we do actual file validation (bytes) and not just extension validation for the uploaded images. Yes, it would take more time. But, since I was just low on the pole, I think I wasn't taken seriously.

Also maybe it wasn't my place to suggest design solutions, and or my approach wasn't as good as it should have been.