Bengal’s criminal investigation department (CID) has written to Facebook in its efforts to track down those responsible for uploading four Internet pictures lampooning chief minister Mamata Banerjee.

If the CID persists with the drive, it will mean that the government is keen to take its crackdown beyond the circulation of unpalatable digital content and to its very source of origin. The CID’s cyber crime cell had earlier written to Facebook and Google asking them to delete objectionable material but never before had it tried to reach the source.

Requests for deleting content considered objectionable or inflammatory are neither unusual nor unreasonable. But attempts are usually not made to trace the source, not only because of the complex nature of the hunt but also because of the futility as someone else can post something else from some other country in the seamless information age.The investigating agency has asked the US-based social networking site to provide IP addresses of the computers from where the four images were uploaded.

CID sources confirmed that the Sonar Kella joke, over which a Jadavpur University professor was arrested last week, was not among the four for which Facebook has been asked to start a probe.

In the letter addressed “To whom it may concern” and mailed to the Facebook headquarters at Menlo Park, California, the CID mentioned a complaint lodged by a Trinamul Congress activist in New Town last week. That Suman Naskar, the Trinamul activist from Mahishbathan, on the fringes of New Town, had filed the complaint was reported on Sunday.

Naskar, in his mid-30s, had mentioned in his complaint that a section of youths had uploaded morphed pictures of the chief minister to malign her character. “We will try to track down those who uploaded the pictures before it flooded the walls of hundreds of Facebook users,” an officer said.