Re-printed courtesy of OzMPS Forums
THE most common question asked by a forum beginner is "How do I post a picture in a thread?" (Yes I asked it myself)
The forum allows you to attach images, but only pictures small in file size and that can be annoying. The best way to post an image is to host it on an "image hosting website" and then link that image to your post.
There are many websites out there that will host your images for you for free, so choose whatever one you like to get started!
Here is a list of some free image hosting websites;
(I will show how to post pictures uploaded to the mentioned websites into your post)
imgur: the simple image sharer
Photo and image hosting, free photo galleries, photo editing
Welcome to Flickr - Photo Sharing
ImageShack® - Online Photo and Video Hosting
Note: You can also link your pictures from Facebook to your post if you like to upload your pictures to there.
Note2: There is a forum app for Android and Apple phones through which images can be posted too
Sign up to your image hosting website, and then upload the image/s you want to put in your post.
IMGUR
Firstly select the image you want, then;
then paste the link into your post and you're done! The way that Imgur sets up it's links is so that the image code is already attached to the location of the link making it easy as!
PHOTOBUCKET
Photobucket sets up its links in a similar way to Imgur so select your image;
and then paste the link into your post. Photobucket is nice because when you click on the link it automatically copies it 
Note: Photobucket has an app for Android (I'm not sure about iOS) and you can upload images through this app, then copy the image tag and paste into your post from your phone
FLICKR
Flickr is a LITTLE different, select your image;
and then your image will appear.
IMAGESHACK
Select your image
Facebook
To upload an image from facebook, copy the image URL
Tapatalk
Lastly there is another way to insert an image into your post and it is with the Tapatalk app. It is available for Android and Apple devices.
It is not a free app, however only costs a few dollars.
It's a great app, allowing you to sign into many forums and gives you alerts on the go
You can see how i'm logged into 4 forums and have elected to receive notifications for various things from each forum.
Open your post, and you will see the screen shot on the left with tapatalk 2, middle with tapatalk 4 (on an android phone) or on the right a shot from an iPhone
It will then ask you how you want to host it, select "Tapatalk Hosted". (or select "Upload to Tapatalk" as seen on the iPhone)
This uploads the image to the tapatalk server and links it automatically from there. Thats why I think this is the easiest way to do things.
In short:
When you click the "Insert Image" icon and paste the URL, all this does is add the tags [IMG ] ... [ /IMG] around the link you posted. So in other words, you can just copy the direct link of the image into your post and write [IMG ] before the link and [ /IMG] after the link (without the spaces in the tag) and you're done.