There are basically two ways to do it. The first way is to download your pictures to another site, and then reference that site back to your post. But if you want to put your pictures directly into your pose this is kinda how you do it.
First off you have to see if your pictures are the right size. Looking at your pictures in your My documents put the curser on them and dont move it. A little thing will pop up and tell you the size of your picture, and what kind of file it is, ie Jpeg. You have to see what kind of file it is and then come back here and click on the attachments thing (looks like a paper clip, to the top of where you write your text). You click on that and a screen will pop up, and it will have a list of file and there max sizes. Then you can see what your files size is and see if your photos are the right size. If they arent the right size then you have to download a picuture resizing software program (google something along those lines and you'll find something, make sure its free though). So if your pictures are the right size, then you go and click one of the browse things, and then you go through your documents and look for your picture that you want to download and then click on it. Then it will come up on that other screen and then you click load.
It would probably be easier if you went through another website and did that, becuase they have bigger file sizes so you would probably not have to do the picture size software thing, cause that can take some time to get the picture the right size.