Look into resizing photos. I would bet you have a program on your computer that will handle it such as "image", "paint" or "photoshop elements". For the web, if you have the choice...you want images to be 72dpi and anywhere from 600-1000 pixels wide. I typically go 800 on the longest side. If you are using a smart phone, you might do a web search about resizing photos with xxxxxxphone.
Also, look into free photo hosting. I used to use imageshack, but they want money now. Photobucket is still a good one I think, but I don't know what's popular. You may have to research them a bit and see which one makes sense to you. With those, they'll let you upload the picture there on their site, and copy a link to paste into your post on forums. Worked really well when I used to do that sort of thing.