How do you guys get your pics to come up big and not just thumbnails??
To actually answer your question, rather than debate the merits of actually doing it:
When making a new post, click the "Go Advanced" button in the lower right corner of the new post box.
Add your picture as you normally would.
You should see a tag added which is the code to add your picture similar to this:
(ATTACH=CONFIG)660560(/ATTACH)
Normally, this would be in square brackets, rather than parentheses. I changed it here so you could see the tag, rather than the picture when I posted this.
Click the little box in the upper left corner of the post formatting bar that has the little A/A in it. This box will toggle between a text mode, which displays the code for the link and "What-You-See-Is-What-You-Get" mode. (That box is also there when you are not in "Advanced" mode, but it doesn't seem to do anything).
When in WYSIWYG mode, you'll see the thumbnail of your picture. Double click that thumbnail to bring up a dialog box where you can choose the size. I use "Medium" a fair amount, since it doesn't clutter up the thread with huge pictures, but still shows some detail that is hard to see in a thumbnail.
NOTE: when using this feature, please be considerate of those of us with slower internet connections. There is generally no need to upload a multi-megabyte photo for online viewing. Downsize your picture before uploading using any one of many available photo editing apps (I use Apple's "Preview" which comes free on their computers). Generally, a file size of a few hundred K is PLENTY. Often 100K or less will do the trick, if you don't need fine detail. You will still have the option to choose a display size for your photos when posting using the above technique.