You need an internet host such as PhotoBucket, imgur, etc. Upload your pictures to the host site. The one I'm most familiar with is PhotoBucket. I create a separate folder there for the pictures I want to upload. Once your pics are in PhotoBucket, when you place the pointer on the picture you want to post, a "tool wheel" will appear in the upper right hand corner. When you move the pointer to it, a list of options will drop down. Click on "get links" and another menue will drop down. Click on the bottom, "img" option and it will change momentarily to read "copied".
Go to your Trad Gang ad where you want to place the picture and right-click and "paste" the link. That's it. If you then look at "preview", you will see your picture as it will appear with your copy in the ad. Sounds confusing, but after you've done it a couple of times it's really easy.
I open separate tabs for Photo Bucket and Trad Gang so both Trad Gang and Photo Bucket are available at the top of the browser toolbar. That way, I can get a link to a pic in Photo Bucket, then open the Trad Gang tab and paste it. I can bounce back and forth selecting a pic and then pasting it in the Trad Gang post until I have all the pics posted.
Probably someone who is more internet knowledgeable can explain it better, but now that you don't need to worry about re-sizing your pictures, it really is a piece of cake.