This is an interesting expression that I came across very recently while reading a Tamil magazine. The literal meaning is that you can't cook the stew by just having a painting of a bottle gourd. Apparently, this proverb has different interpretations and is applicable to a variety of contexts. However, the most often implied meaning goes something like this:
"Theoretical or textbook knowledge (a picture of a bottle gourd) alone is not enough. Practical know-how (metaphorically refers to a real bottle gourd) is also important to accomplish things (making the stew)".
In short, knowledge gained through practice always trumps knowledge gained by reading textbooks alone.
I searched and found an expression - "A little knowledge is a dangerous thing"[TFD] but it emphasizes being over-confident after gaining a small amount of knowledge.
For those interested in knowing the actual Tamil proverb, it is "ஏட்டுச் சுரைக்காய் கூட்டுக்கு உதவாது"