The prosecution of Cyber Libel in the Philippines is primarily governed by Republic Act No. 10175, otherwise known as the Cybercrime Prevention Act of 2012, in relation to the Revised Penal Code (RPC). Because the medium of the offense is digital, the evidentiary requirements are more stringent than traditional libel, necessitating compliance with the Rules on Electronic Evidence (REE).

I. The Elements of Cyber Libel

To successfully file and prosecute a case, the evidence must establish the following four elements beyond reasonable doubt:

Allegation of a Vice, Defect, or Crime: There must be a defamatory imputation that tends to cause dishonor, discredit, or contempt of a natural or juridical person.
Publication via Information and Communications Technology (ICT): The statement must be made public through the internet, social media, or any other digital platform.
Identifiability of the Victim: A third person must be able to recognize that the defamatory statement refers to the complainant.
Existence of Malice: The statement was made with a "dishonest purpose" or "ill will." In cases involving public figures, "actual malice" must be proven—meaning the defendant knew the statement was false or acted with reckless disregard for the truth.

II. Essential Documentary and Digital Evidence

Unlike physical print, digital content is ephemeral and easily deleted. The following evidence is crucial for a filing:

1. Screenshots and "Functional" Captures

While simple screenshots are common, the courts prefer evidence that establishes the source.

Contextual Integrity: The screenshot should include the URL, the timestamp, the profile name/handle of the poster, and the engagement (likes, shares, comments) to prove publication.
Authenticated Copies: Under the REE, an electronic document is admissible if it is shown to be what it purports to be.

2. Verification of Digital Identity

A major hurdle in cyber libel is proving that the person who owns the account is the one who actually posted the content.

IP Address and Logs: If possible, obtaining the IP address through a court-issued Warrant to Disclose Computer Data (WDCD) can link the post to a specific internet service provider (ISP) and subscriber.
Circumstantial Links: Evidence such as the use of a personal mobile number for account recovery, or the posting of personal photos/information that only the account owner would possess, can help establish identity.

3. Formal Demand Letter

While not strictly a requirement for the crime itself, a demand letter for the removal of the post and a public apology serves as evidence of the complainant’s attempt to mitigate damage and can be used to further demonstrate the persistence of the respondent’s "malice" if they refuse to comply.

III. The Rule on Authentication

Under the Rules on Electronic Evidence, electronic documents (including social media posts and emails) must be authenticated to be admissible. This is done by:

Evidence that the electronic document had been integrity-checked by a digital signature or other methods;
Evidence that the document is what it claims to be (e.g., through the testimony of someone who saw the post live); or
Other methods of authentication authorized by the Supreme Court.

Note: A mere printout of a Facebook post is often considered "hearsay" unless the person who made the printout or saw the original post testifies to its accuracy.

IV. Procedural Requirements

1. Jurisdiction and Venue

Cyber libel cases can be filed where the complainant actually resides at the time of the commission of the offense or where the defendant resides. However, the Regional Trial Court (RTC) designated as a Cybercrime Court has original and exclusive jurisdiction over these cases.

2. Prescription Period

A critical legal nuance is the prescription period. While traditional libel prescribes in one year, there has been significant legal debate regarding Cyber Libel. The Supreme Court (in Tolentino v. People) clarified that the prescription period for Cyber Libel is one (1) year, aligning it with the RPC, despite the higher penalties involved.

3. The Preliminary Investigation

The complainant must file a formal Affidavit-Complaint before the Office of the City or Provincial Prosecutor. This must be accompanied by the Affidavits of Witnesses—individuals who saw the post and can testify to the identity of the victim and the damage caused to their reputation.

V. Defenses and Exemptions

When preparing evidence, one must anticipate the "Justifiable Motives" defense. Under Article 354 of the RPC, a defamatory imputation is not actionable if:

It is a Privileged Communication: Such as a private communication made in the performance of a legal, moral, or social duty.
It is a Fair and True Report: Made in good faith, without comments or remarks, regarding official proceedings (judicial, legislative, etc.) which are not confidential.