If you need a picture of rahat irrigation, the traditional Indian method of irrigating fields, then the first place to try would be Google Images, which is where I found the picture you see below:
For pictures you can use for free, try Wikimedia Commons. Almost all the pictures on this site are in the public domain, and can be used how you wish, although it can be may be more difficult to find a good picture of rahat irrigation.
Another free image site is morguefile.com, which is aimed more at the artistic and creative community.
If you're willing to pay for a picture of Indian irrigation methods, try an established image stockist site such as photosindia.com or gettyimages.com.
Several YouTube users have posted film of the rahat irrigation process, such as this one, which might be of help:
