iter. The image will be
counted as one character in character counts, and when obtaining
the buffer contents as a string, will be represented by the Unicode
"object replacement character" 0xFFFC. Note that the "slice"
variants for obtaining portions of the buffer as a string include
this character for pixbufs, but the "text" variants do
not. e.g. see gtkTextBufferGetSlice and
gtkTextBufferGetText.gtkTextBufferInsertPixbuf(object, iter, pixbuf)objectiterpixbuf