Usually the phrase refers to the way a student copies another's answers in a school test or exam - word for word thereby usually getting caught by the evaluating teacher.
The phrase implies that the copy cat doesn't have her own brains or use it if present even a little bit, and blatantly copies this way.
The expression derives thus:
If she finds a fly (makhi, Hin.) on the source answer-sheet at the moment of copying, she will even copy the shape of that fly into her own answer-sheet or drawing in the test.
Makhi has gotten corrupted in Kannada usage as 'makki'