Insert text with image into a SharePoint LIstItem

I do the creation of items in SharePoint, with a WPF/C # app, as in the example:

using System;
using Microsoft.SharePoint.Client;
using SP = Microsoft.SharePoint.Client;

namespace Microsoft.SDK.SharePointServices.Samples
{
    class CreateListItem
    {
        static void Main()
        {   
            string siteUrl = "http://MyServer/sites/MySiteCollection";

            ClientContext clientContext = new ClientContext(siteUrl);
            SP.List oList = clientContext.Web.Lists.GetByTitle("Announcements");

            ListItemCreationInformation itemCreateInfo = new ListItemCreationInformation();
            ListItem oListItem = oList.AddItem(itemCreateInfo);
            oListItem["Title"] = "My New Item!";
            oListItem["Body"] = "Hello World!";

            oListItem.Update();

            clientContext.ExecuteQuery(); 
        }
    }
}

The issue is that in the "Body" column, I would have to insert a content coming from a RichTextBox, where it is possible to insert texts with images.

I have not found a way to insert the text and images, added As in a word document, to this column. Getting the RTB content with textRange results in converting the image to hexadecimal, which doesn't suit me.

I know that it may be necessary to save the images in a directory within sharepoint and reference them in the text, like an index or something, but I did not find documentation and I have no idea how to do.