When Tracing Is Not OK
I don't want you to trace artwork unless you significantly change it to make it your own. Don't just copy and slightly manipulate.
So this is NOT OK:
Source to trace (link)
Traced copy
The lines in the traced copy are identical to the ones in the source image. It's just copied and flipped.
If you're worried about where to draw the line between what's OK and what isn't, just ask me.