Okay, posting pictures. First, I'm going to just manage expectations by saying these suggestions are probably not going to work for everyone - I can't replicate everyone's computers, operating systems or browsers. I also am not part of the development team, or mandating how you should post your images, I'm just sharing what works for me.
So, you have your image and you want to display it on the boards. I am going to assume for the sake of argument you have permission to do so and aren't breaking any copyright agreements. How to get other people to see it? Well, if it's a file on the web, you can link directly to it by use of this icon here:

Pate the image URL into the box it brings up:

Be nice if it always worked but frankly, it seems pretty hit and miss. As you can see, this has worked to load wikipedia's photo of Alonso...

...but it failed to display Wikipedia's file pic of Botticelli's Birth of Venus. Incidentally, be aware that certainly back in the old days of the internet, linking directly like this, was, and actually still is by many, seen as a bit of faux pas because it eats the host site's bandwidth. For this reason, I always use my own private photohosting account because a) I'm not eating anyone's bandwidth and b) it actually always works.
I would love at this point to give you the full rundown on all the photo sites out there with their pros and cons. I cannot. I can tell you that I used to use Photobucket. It's free and quite user friendly. I also don't recommend it because certainly when I was using it, the bandwidth allocated to each photo for public viewing was pretty tiny. I use imgur because it is a) free and b) pretty reliable and I know how it works. It has a community and a front page of often tasteless photos which I just ignore and go into my account.
Posting from Imgur,
1) Upload your picture into your account. If it is already on your hard drive, click 'computer' as shown below to open up a box which will allow you to browse your PC to select the picture file and upload..

2) To display on the boards here, click on the image you now have in your imgur images like so:

3) Copy the highlighted line to the right of the picture. This is the bulletin board code of your picture.

4) Press paste into your Autosport forums reply post.
5) Preview to check your image isn't absolutely enormous. If it is, there's a couple of things you can do to change the display size. You can use the thumbnail facility circled in this image.

It uploads well, a thumbnail instead of the whole image.
Or, and this is what I do, you just go to the code you've pasted in. Look at the file extension, which will usually be .JPG or .PNG etc. If you manually add the following letters S, M or L Just before the .JPEG bit, it makes well, small medium or large versions of the file display.
For example - and I've manually changed the 'I' of IMG for the number 1 here to show the code - I start with:
[1MG] http://i.imgur.com/4dsTe88.jpg[/1MG],
... But if I add an 's' like so: [1MG]http://i.imgur.com/4dsTe88s.jpg[1IMG] then it will display like this:

For 'm'

'L'

There. As I say, I know in advance this will not help all of you but I hope it may help at least someone.