There are many others than just these...but these will get you started.
Once you have chosen a place to upload your pictures, go ahead and upload them to the site. Usually there will be a browse button you can use to help you find your pictures. If you have a lot of pictures to post, I would choose one of these sites that allows you to do multiple uploads at a time.
Don't close the web page while the pictures are uploading. It will sto the upload. You can open a new browse window or a new tab and go to a website from there, just don't close the upload page.
Once they are uploaded, the site usually gives you code to copy and paste into the forum that will create thumbnails. Clickable thumbnails are preferred. It doesn't mess up the formatting of the thread and people can quickly choose which pictures they want to see instead of scrolling through huge pictures, waiting for them to load, etc.
Alternatively, you can, of course, use the forum's Upload attachment option [You must be registered and logged in to see this image.]when you want to post a photo
P.S. This topic is just for viewing and reading. If you follow these guidelines but still have a problem related to 'uploading pictures', just open a new topic. Thank you!