We're going to be using Imgur as it's a very quick straightforward process. In Imgur, upload your image - and resize it, To see images nicely in a board, you'll need a minimum of 400px width and a maximum of around 650px width.

You'll need to click on the three little dots, then 'edit' and then resize so that there's a sensible width.

You'll then need to (important) right-click on the image and 'copy image address'. Then either paste it into a holding doc or in your browser and...

...navigate over to your thread, and open up the reply button.

Click on the little yellow photo icon at the top of the reply box

paste your link using cntrl+v or your menu commands of edit paste

Then, just check that your image is showing correctly, and that it's a sensible size by hitting 'preview'

This won't help you in posting a hi-res image, with more detail, but it will help you share your image in a way that's more accessible to people than attaching it as a file :)

You can resize images in a desktop editor, too, of course.

Once you've resized, you can upload to flickr or whichever stream suits you and collect the link to post on the board :)

Please note - if you have an image you wish to protect (Intellectual Property) or tag with a particular creative commons licence, or send out for publication, be wary. You might want to host this on your personal website or social media instead, as most editors mind this less. Or, if you're very, very keen to protect the image, try an adobe photoshop site, as their software automatically prevents people from downloading full-res images.