The most straightforward way would be to modify the RTF code to insert the picture yourself.
In RTF, a picture is defined like this:
‘{‘ \pict (brdr? & shading? & picttype & pictsize & metafileinfo?) data ‘}’
A question mark indicates the control word is optional.
“data” is simply the content of the file in hex format. If you want to use binary, use the \bin control word.
For instance:
{\pict\pngblip\picw10449\pich3280\picwgoal5924\pichgoal1860 hex data}
{\pict\pngblip\picw10449\pich3280\picwgoal5924\pichgoal1860\bin binary data}
\pict = starts a picture group,
\pngblip = png picture
\picwX = width of the picture (X is the pixel value)
\pichX = height of the picture
\picwgoalX = desired width of the picture in twips
So, to insert a picture, you just need to open your picture, convert the data to hex, load these data into a string and add the RTF codes around it to define a RTF picture. Now, you have a self contained string with picture data which you can insert in the RTF code of a document. Don’t forget the closing “}”
Next, you get the RTF code from your RichTextBox (rtbBox.Rtf), insert the picture at the proper location, and set the code of rtbBox.Rtf
One issue you may run into is that .NET RTB does not have a very good support of the RTF standard.
I have just made a small application* which allows you to quickly test some RTF code inside a RTB and see how it handles it. You can download it here:
RTB tester (http://your-translations.com/toys).
You can paste some RTF content (from Word, for instance) into the left RTF box and click on the “Show RTF codes” to display the RTF codes in the right RTF box, or you can paste RTF code in the right RTB and click on “Apply RTF codes” to see the results on the left hand side.
You can of course edit the codes as you like, which makes it quite convenient for testing whether or not the RichTextBox supports the commands you need, or learn how to use the RTF control words.
You can download a full specification for RTF online.
NB It’s just a little thing I slapped together in 5 minutes, so I didn’t implement file open or save, drag and drop, or other civilized stuff.