It's ok to use references! Yes, I know you want to draw everything from your imagination, but it's not cheating to find a photo to help. Also, don't use your reference photos as law. Deviate from them, use them to guide you, not for you to replicate.

I can add to this, technically when you draw "from imagination" youre taking from your visual library of references that you have in your head, using references expands this library. If you struggle with drawing from imagination, use a reference, even if you dont, use a reference, build the library!