Bonjour ,
J'ai utilisé le Control Html EditorExtender dans ma page aspx
<ajax:HtmlEditorExtender ID="HtmlEditorExtender1" OnImageUploadComplete="HtmlEditorExtender1_ImageUploadComplete"
TargetControlID="txt_DescriptionCMS" DisplaySourceTab="True"
runat="server" EnableSanitization="False" >
<Toolbar>
<ajax:Undo />
<ajax:Redo />
<ajax:Bold />
<ajax:Italic />
<ajax:Underline />
<ajax:StrikeThrough />
<ajax:Subscript />
<ajax:Superscript />
<ajax:JustifyLeft />
<ajax:JustifyCenter />
<ajax:JustifyRight />
<ajax:JustifyFull />
<ajax:InsertOrderedList />
<ajax:InsertUnorderedList />
<ajax:CreateLink />
<ajax:UnLink />
<ajax:RemoveFormat />
<ajax:SelectAll />
<ajax:UnSelect />
<ajaxelete />
<ajax:Cut />
<ajax:Copy />
<ajaxaste />
<ajax:BackgroundColorSelector />
<ajax:ForeColorSelector />
<ajax:FontNameSelector />
<ajax:FontSizeSelector />
<ajax:Indent />
<ajax:Outdent />
<ajax:InsertHorizontalRule />
<ajax:HorizontalSeparator />
<ajax:InsertImage />
</Toolbar>

</ajax:HtmlEditorExtender>

et dans .cs j'ai fait ce code
protected void HtmlEditorExtender1_ImageUploadComplete(object sender, AjaxFileUploadEventArgs e)
{


string filePath = "~/Administration/Image/" + e.FileName;

// Save uploaded file to the file system
var ajaxFileUpload = (AjaxFileUpload)sender;
ajaxFileUpload.SaveAs(MapPath(filePath));

// Update client with saved image path
e.PostedUrl = Page.ResolveUrl(filePath);
mais ça marche pas je veux upload/ save l'image :/