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"
Best Answer
Here's one that highlights the problem with relying only on the theoretical at the expense of the practical:
(Thanks to @DCShannon for the snopes link for attribution.)