In the Lamrim teachings it says that just seeing an image of a Buddha places a potentiality on the mind that is a definite cause of enlightenment, and which nothing can destroy. This potentiality is likened to a tiny diamond that is swallowed and passes through our body intact, uncorrupted by all bodily impurities. Because Buddha is a completely pure object wholly beyond samsara, the imprint of seeing a Buddha image has a special quality that does not belong to samsara, and even if it is placed in a mind filled with delusions it can never be corrupted or destroyed. This imprint or potentiality is also compared to a spark with the power to ignite a fire that in time consumes a haystack the size of the world. We have seen how, due to the imprint of seeing a stupa, Shri Datta was able to generate the wish to enter the path to liberation and, by practising Dharma, burn away all the delusions in his mind.
From these examples we can understand how seeing images of Buddha has the same function as seeing actual living Buddhas. In a similar way, making offerings and prostrations in front of Buddha images has the same function as making offerings and prostrations in front of living Buddhas, and accumulates the same amount of merit. This is why it is considered so important to have a large and beautiful statue of Buddha in Buddhist temples, for then anyone who visits the temple and sees the statue is creating the cause to attain liberation and enlightenment.
Pg 33 -34 Eight Steps to Happiness – Venerable Geshe Kelsang Gyatso