EtherPEG is described as 'free program for the Macintosh that shows you all the JPEGs (and GIFs) going by on your network' and is a Network Analyzer in the Network & Admin category. There are seven alternatives to EtherPEG for Windows, Linux, Android, BSD and Mac. The best alternative is Wireshark, which is both free and Open Source. Other great apps like EtherPEG are tcpdump (Free, Open Source), PCAPdroid (Free, Open Source), Driftnet (Free, Open Source) and York (Free).
Wireshark is the world's foremost network protocol analyzer. It lets you capture and interactively browse the traffic running on a computer network. It is the de facto (and often de jure) standard across many industries and educational institutions.
tcpdump is a common packet analyzer that runs under the command line. It allows the user to intercept and display TCP/IP and other packets being transmitted or received over a network to which the computer is attached.
PCAPdroid is an android app to capture the phone traffic and analyze it remotely (e.g. via Wireshark). The traffic can be easily downloaded from a remote device thanks to the integrated HTTP server, or streamed to a remote UDP receiver.
HttpCanary supports packets capture and injection. With this app, you can test your mobile Rest APIs very very easy. Besides, HttpCanary provides multiple view browsers, such as raw viewer, hex viewer, preview viewer and so on.