If you use a phone like I do (only source if internet I’ve got) it’s simple.
Just click on the middle white button at the bottom that says “upload file or photo”

That’ll bring up this pop-up. Then just hit “photo library” for the already taken pictures or you can take a new one as well obviously.

Selecting the photo library tab just goes right to the phones phot gallery.

If you’re posting from a PC I’m assuming it’s gotta be relatively similar but I haven’t got a clue first hand.
Just click on the middle white button at the bottom that says “upload file or photo”
That’ll bring up this pop-up. Then just hit “photo library” for the already taken pictures or you can take a new one as well obviously.
Selecting the photo library tab just goes right to the phones phot gallery.
If you’re posting from a PC I’m assuming it’s gotta be relatively similar but I haven’t got a clue first hand.