it is better to use the 'Finder' since it has more control.
I wrote this code which to replace the text "[sig]" with a certain image. Should be suitable example.
Code
WPRichText1.Finder.ToStart;
while WPRichText1.Finder.Next('[sig]') do
begin
WPRichText1.CPPosition := WPRichText1.Finder.FoundPosition;
WPRichText1.Finder.FoundText := '';
WPRichText1.TextObjects.InsertCopy(Image1.Picture.Graphic);
end;
WPRichText1.DelayedReformat;
