Here's how I post photos on TrumpetBoards:
Make sure there's a photo on the hard drive, whether in Pictures or Downloads.
Use https://fileminimizer-pictures.en.softonic.com/download to compress the file.
Click on the Upload Image icon (second from the right above the message body in Reply on TrumpetBoards).
, Select the FILEminimizer version of the image.
Click Open (my example result below).
Screenshot 2023-12-18 192943 (FILEminimizer).png