On the “Files” tab you can configure how files inside archives should be handled. You can define which app should be used to open files when double-clicked (or viewed). You also can set which preview mode to use for file types: Default, Text, Image, PDF, or Quick Look.
The file type is determined by the filename extension which is matched against a regular expression. In the simplest form, just add the extension (e.g., jpg) in the “Extensions” textfield. Multiple extensions can be configured together with vertical bars between them (e.g., jpg|jpeg|png). Another example would be to handle all files with numeric extensions: [0-9]+