There are many sites, but I'll explain how to use one of the most used:

http://imageshack.us/


Once on this site, you note a "parcourir" or "Browse" button (depending of your browser language), and juste below, allowed picture format which can be uploaded from your computer, to the web:
.jpeg ; .jpg ; .png ; .gif ; .bmp ; .tif ; .tiff ; .swf

The maximal picture's weight authorized by Imageshack: 1024 Ko
This is really enough for all pictures, above, it will cause slow down to the page's loading.



Clic on "Parcourir..." or "Browse" (It depends of your browser's language) you access so to your computer. You just have to look for your picture and select it, clic on "open":




Now, just choose "Host it!" and your picture will be uploaded from your computer to the server.

A new page is opened with a few links, they are all links to your pictures(but we won't use them all):



-Hotlink for forums 1 et 2: these two lines are the same, do a copy/ paste of these lines to directly display a picture on a post.

-Hotlink for websites: this is HTML script, allow you to host pictures for your web pages, or for the headers, portal, or forum's description.

-Show image to friends: send this line to your friends or contact, and they'll be able to use all the lines to display the pictures.

-Direct link to image: a direct link to the pic, this is the most useful, this is the line that you'll copy/ paste to your admin panel for your logo and picture management. It can also be used to link an avatar on the "link to off-site avatar" field.
In fact, I personnaly always use this line, and I just have to add my tags, BBcode in a post, or HTML to display my picture.
So with this line:

In BBcode:

Code:

[img]direct link[/img]

In HTML:

Code:

<img src="direct link">

On top of the page, you can see "Upload another image", if you have to upload other pictures, you just have to click on it or on the frog logo.


Above 200 or 240 px from height, other lines appear:




The problem with large pics, is first, that they deform your board, and second, people with low speed connection won't appreciate to wait the load of your board's page if you display it directly on a post.
Imageshack provide a reduction of the pic, with a link on it to the real sized pic.

-Thumbnail for Websites: same thing that hot link, but with a thumbnail of the pic. This display the thumb where you write it, and there click on the thumb, the original sized pic open on a new page. This is HTML script, not used in a post.

-Thumbnail for forums 1 et 2: thumbnail for a post. Simply copy/ paste it in your post to display the reduction with the link on the real sized picture.

If thumbnail are proposed, you better have to always choose it to many reasons.

This is what gives a thumbnail, clic on it: