Using a site like
Imgur ("other services are available") makes it very easy to post an image to WP.
You set up a free account, to which you can upload images by browsing or by drag-n-drop - into your own private image area there.
Posting an image here is little more than clicking on it in your Imgur stash, then clicking a button next to it to copy the information required to post the image to WP.
In your WP post it's just a case of pasting into it to plant the ready-formatted image link, adding any required text, then clicking "Submit" as usual.
No images (apart from avatars) are stored here because of the storage space required for them, along with the accompanying increase of hosting costs (which Alex continues to pay at no charge to members).
But even if they were stored on WP, the process required to display them in a post would be very similar to that used for Imgur: there has to be
some method of indicating where the image is located and as it's not possible (on any online service) to simply point at an image stored locally on your device, using a link to an image publically available elsewhere is the easiest solution.
Avatars are the only image type uploaded directly to WP - they're small and the storage doesn't amount to very much.
As there's an "Upload from your machine" button in a member profile to select an image, the biggest difficulty then is editing it so it fits the size required by WP: 130 pixels wide by 160 pixels high, with a file size not exceeding 3719.87 KiB.
I'm quite happy to help with this.
Alternatively websites exist that allow anyone to upload pictures stored on their devices to said website that will give a postable URL that WP can use for thread posts.
Avatars are completely different but editing them will always be annoying.