Which of the following indicates a PNG file signature?

Most standard file formats reserve a fixed sequence of bytes, called a file signature or magic number, at the very start of every file of that type. Because this sequence never depends on the file's name or extension, forensic examiners and operating systems read it directly from a file's first bytes to identify the file's true type, even when the extension has been altered, removed, or is missing.

1. FF D8 FF E0 pairs the two-byte marker FF D8 with the two-byte marker FF E0; two-byte FF-prefixed markers of this kind introduce the segments of the JPEG/JFIF image format, so this sequence opens a JPEG file, not a PNG file.

2. 50 4B 03 04 opens with the ASCII letters “PK” (50 4B, the initials of the format's original author) followed by the header-type bytes 03 04; this four-byte opening is the ZIP local file header used by a non-empty ZIP archive and by many ZIP-based containers (DOCX, XLSX, JAR) — an empty ZIP archive instead begins with the end-of-central-directory signature 50 4B 05 06 — so it also does not open a PNG file.

3. 89 50 4E 47 is the first four bytes of PNG's complete eight-byte signature, 89 50 4E 47 0D 0A 1A 0A. The leading byte, 0x89, is deliberately chosen outside the printable-ASCII range so that a file corrupted by a 7-bit-only or text-mode transfer becomes immediately detectable; the following three bytes spell the ASCII letters “PNG”; and the remaining four bytes (0D 0A 1A 0A) add a carriage-return/line-feed/EOF/line-feed check that catches line-ending translation errors as well.

Cross-checking each option against its own format's convention confirms the mapping is exclusive: JPEG files always begin FF D8 (never 89 50), and ZIP-based files always begin 50 4B (never 89 50). So among the sequences offered, only 89 50 4E 47 opens with the bytes PNG's specification defines as its signature.

Therefore, 89 50 4E 47 indicates a PNG file signature, and “None of these” does not apply.