Before you can insert images in posts, you must have at least a Jr. Member rank. You can see the full details in the original thread created by @theymos. Then, once you reach that rank, you can use image hosting platforms like TalkImg to upload your images.
As for merits, you just have to contribute here, you can get them in various ways, @katanic97 has given some, for additional ones, you can also join BC.Game [CHALLENGE] Run A Bitcoin Node: 14 Days To 14 Merits.
Source:
1.
https://bitcointalk.org/index.php?topic=2818350.02.
https://talkimg.com/3.
https://bitcointalk.org/index.php?topic=5480200.0- Ammar M. A.