1. Go to http://imageshack.us
2. You have there a space (be sure that file is checked, not url) and near it Browse. Click it. Then you select the picture you want to upload from your computer. Be sure that none of the boxes above (resize and remove resolution bar from thumbnail) are checked, only if the picture is too big (let's say wallpaper size) then check the resize box and select the size you want it to make.
3. Press Host It and wait.
4. In a few moments/minutes (It depeds on how fast is your internet and the size of the picture) a new page will appear where you have a smaller example of the picture you uploaded and some links for your picture:

-Thumbnail for Websites
-Thumbnail for forums (1)
-Thumbnail for forums (2)
-Hotlink for forums (1)
-Hotlink for forums (2)
-Hotlink for Websites
-Show image to friends
-Direct link to image

*If the picture is too big and you didn't resize it then click on the link near Thumbnail for forums (1), copy it and then paste it here as it is.
*If the picture has a normal size then click on the link near Hotlink for forums (1), copy it and then paste it here.
*Or you can open Add Reply and there you have IMG, click it, and the Explorer User Prompt will appear. Paste there the link and click ok.