What exactly are the sources of WebImageText dataset?

[andrey-savov]

In this paper there is only a vague description about the WIT dataset:

... we constructed a new dataset of 400 million (image, text) pairs collected form a variety of publicly available sources on the Internet.

Can you enumerate specific sources and methods used to acquire the images?

[ShilpaGopal]

How are texts engineered? Paper talks about prompt engineering for tasks datasets but not for the 400M training dataset!!

[placeforyiming]

Looking for more information here