The forum has an attachment feature where you can upload the images you want to share, but there is a limit (as I pay for the hosting and there is only so much space).
The best way is using a mix of flickr.com and the [ img ] tags. Here is a step by step on how to do it,
1. Register to Flickr
Go to https://www.flickr.com/ and register a new account (or login). It is free and easy to sign up to (as long as you accept ads).
2. Upload your photos
Click on the upload button at the top of the page. It is the icon of a cloud with an arrow in,
3. Upload your files
You will see a screen asking you to either drag and drop your files in, or click and search. Do whichever you would like, but drop the images you want to upload into the screen and it will upload them.
4. Check and finalise upload
You will now see all of the image you have uploaded. You can edit, remove or tweak your images here before finalising the uploads.
When you are happy, click the upload button on the top right of the screen.
5. Choose your image to post and click the share button
Once you have uploaded you images you will see them all in your photostream. From here click on the image you want to post and click on the share button on the bottom right of the image (red arrow below).
6. Check size and copy BBCode
Once you have clicked Share you will be shown a screen where you can select how to share the image. Click on 'BBCode' and make sure the size is correct. The copy the code from the window.
7. Strip out the [ url] section of the code.
You could just paste that code into the forum post and it would work, but to post without a link back to Flickr you can strip out the link by removing all of the code with [ URL ] around it. The link should look similar to the below once done.
Once you have done that you can post onto the forum and your image should work!