First you have to upload your photo to an online hosting service like Flickr, Photobucket or TinyPic.
I like Photobucket because it is very simple to create the tag to import your photo onto Skyscraperpage.
In any event, every photo stored online in a hosting service will have a unique identifier (a URL). You just have to get the URL for your photo, paste it into your post, and make sure that the URL is enclosed by [img] and [/img].
If you do this then your photo gets displayed.
It really isn't complicated, but you will likely have to play around a little bit in order to see how the coding works. If you want, just click on the "quote" button on the bottom right of this post and look at the structure of my post. You will find the code used to display this photo between the [img] and the [/img] imbedded in my post. This will let you know what the photo's URL actually looks like. Once you know this, it will be easy to get the URL for the photo you want to post from your own hosting service. That's basically how I learned to do it. I'm not a techie, but I have done some basic programming in the past, so I know how things work (to some degree). It's not that difficult really.
In any event, I drove by this evening and snapped a picture myself.
I must say that the sign is surprisingly small. There is a notice in the store window stating that Tommy will open in it's new location in "late July".