I want to send screenshots and images in chat. How can I achieve that?
Use the "upload" button. You'll have to take the screenshots yourself (the PrntScrn button on most computers)
Looks like there's a rep requirement for using the "upload image" button, it seems to kick in at 100 rep. You can still post images though. Upload it using the "upload image" button on the main site and post a link in chat.
If the image you want to send is online, then just send the link into chat. If it ends in a supported image type then it will be one-boxed. I know that
.png all work for example.
If not, a popular way to get the image online is to use imgur and upload it there then share the url.