You can post pictures from virtually any website (as long as they're not copyrighted). The three places I use the most to post my photos are Photobucket, Facebook and the horse rescue website (where I've uploaded my pictures).
To post from a website other than Photobucket:
It really helps to have two tabs open, one with your post and the other with the picture you want to post.
Go to the page (I used Facebook for the first picture) and the picture you want to post. Right-click on the picture. Click "Copy Image Location".
Open your post, and click on the "Insert Image" icon.
Press Ctrl+V on the keyboard to paste the image location in the "Image URL" box. Click "Insert Image".
I'm not sure what the "Alt Text" box is for.
Okay, those instructions were for posting from a website like Facebook, Google, etc. Here are instructions for posting from Photobucket (Flickr and other photo hosting sites should be similar).
Open two tabs, your post on the forum and your Photobucket library. I'm assuming that your photos are already uploaded to Photobucket from your hard drive.
Go to Photobucket and click on the "Direct" box for the picture you want to upload.
Press Ctrl+C on your keyboard to copy the Direct Link.
Open your post on the forum and click on the "Insert Image" icon.
Press Ctrl+V to paste the Direct Link into the "Image URL" box. Click "Insert Image".
And you're done! If you need help, don't hesitate to ask.
Dani and Zach ---------- FIDS: Taz (Cockatiel), Chewy (Quaker) and Lily (Budgie); Bilbo (Dog); Diablo (Cat); Mr. Newt; Fish; Camelia aka Cami (Horse); Pork Chop (Guinea Pig) Rehomed: Mickey the pigeon, Gypsy the horse, and 4 of the Jackson 5 (Diamond Doves) RIP: Arnie, Conan, Sammy, Petey, Ms. Praying Mantis, Tito, Pico, Mantis Shrimp, Fuzzy Lionfish, and Phoenix