First off, you want to make sure the photo you select is not too big for the GW server. I find that a photo that is approx. 900x600pixels is an ideal size. If your photo is larger you can easily resize it in a photo editing program.

If you don't have a photo editing program I would recommend "Photoscape", which is a free download from Google. As far free programs go, I think you will find Photoscape to be a very powerful yet extremely user friendly program and I might add, it is totally free of spam or pop-ups asking you to upgrade to an expensive paid program.
In photoscape you select the "editor" then open your photo to the workspace. You can perform a number of different post processing routines or you can just click on the tab that says "resize", click 900 and then hit "save as" and give the photo a new filename or an extension on the original name. It will automatically reduce your photo to 900x600pixels and save it to your normal photo files. (It is important to give the photo a new filename or an extension on the existing filename or the program will reduce your original and you may not want that to happen. BY giving it a new name it will save the reduced file and still maintain the original as an archive file.)

To upload an image on GW you must first post the photo to an online "Image Hosting site"

If you run a search for "Free Image Hosting" sites you will find literally dozens of them. I personally use "Photobucket", which is a free service that I find extremely user friendly.

Once you open an account on Photobucket you can logon and begin uploading your photos. When you hit UPLOAD it will open the photo files on your computer and you select the photo you want to upload. As soon as the photo is uploaded it will appear as a thumbnail on your Photobucket homepage. You can then sort the photos on your homepage into separate folders or just leave them on the homepage.
If you place your cursor over a thumbnail a box will appear below the thumbnail and you will see a box marked "HTML CODE"

To copy the HTML code you place your cursor on the code then you can paste that code into the text of a reply in the forum and the photo will appear.

Here is a little trick. If you want to upload more than one photo to GW copy the HTML code and paste that on your word Pad program, then when you switch from Photobucket to GW you can write your comments, then copy all the HTML codes on your wordpad and paste them into your text.

Sometimes i write my entire reply on the wordpad, add the HTML codes then go to GW and just copy and paste the entire wordpad page onto the forum input box.