That's hot linking and is frowned upon to the point that some sites will block it. You might be seeing the cached version you post over here but everyone else gets a broken image.

Far better to use a hosting services. You could use Pixelfed but it could get a bit messy and it is designed as an Instagram replacement. You've be better off using a dedicated image host:

• Lensdump.is my general image host that I use for all sorts of bits and bobs.
• Catbox hosts images and videos - I use it for the latter.

If it's our own picture, should we use imgur instead of uploading it here? I hadn't done it that way because I wasn't sure if that would let the picture be an expandable thumbnail or if you'd have to click through to imgur to see it

Edit: another question, I see the post language marked as English, when should I be selecting a language for my posts and/or comments, or is it not necessary

They can handle the disk space. Images are small and even smaller when compressed