Function parseAPP13

Parses APP13 (Photoshop IRB) segment for IPTC metadata.

APP13 contains Photoshop Image Resource Blocks (IRB), each with:

• Signature "8BIM"
• Resource ID (2 bytes)
• Pascal-string name
• Data size + data

The IPTC/IIM data is stored in resource ID 0x0404.