How do sites like flipkart postergully posterduniya get licence to reproduce images for posters Is it legal to sell print any image off the internet to make sell-able posters?

Answer 1

No, it is not legal to make sell-able posters based off of random images from the internet.

Every piece of artwork or photograph requires permission from it's original creator or current copyright holder before it can be reproduced.

Even in the case of very old artwork with expired copyrights, you would need to obtain your own copy or photo of the work in person in order to create legal copies. Creating an artwork based on someone else's photo of a piece of art still violates the copyright of the current photo even if it does not violate the artwork's expired copyright.

As for websites with large collections of images, assuming they are following the law they would acquire the license rights from the current copyright holders or more often buy large batches of license rights to entire collections through brokers.

Clipart and stock photo companies often have thousands of images which can be licensed for reasonably cheap prices if purchased in bulk. Many of them often without recurring royalty payments. So a one time fee may allow the buyer to reproduce the work either forever or for a certain number of years, or up to a specific volume, often numbering in the thousands.

In the case of companies which produce posters based on art that you provide, the terms of agreement usually stipulate that the buyer must have the right to production and they act only as the middle man to supply the equipment for production.