You attached the photo, so you're on the right track. If you don't want the forum to host photos, you should find a hosting site like tinypic.com or something and upload your photos there. Once you have uploaded them, copy the Direct Link to Layout link provided for your photo, and then use the [IMG][/IMG] tag in your post. I recommend cropping high res photos before uploading them or use a SPOILER tag if you want to keep them high res (I used both tags below as an example ).

If you have attached the photo to your post like in this thread, the way to insert the picture directly into your post is to first preview your post before you submit. Then right click the attached file shown in the preview, and select Open in New Tab (or Window). When the full size image displays, right click on it and select Copy Image URL (you can do this with any image posted online, but note that you might be copying the link to a thumbnail rather than the full size image so be careful about that - for example if you don't open your attach photo in a new tab or window and just click Copy Image URL on the small thumbnail, you won't get the full size pic). Once you have copied the URL, you just put that inside your IMG tag.