The word image is an unbound morpheme, not a bound morpheme, because it is a word by itself. In any language,a morpheme is a unit of meaning. A word is an unbound morpheme because it is a unit of meaning when it stands alone, not bound to anything else. Image is a morpheme in "imagination," but, because image is a word in itself, image is an unbound morpheme, rather than a bound morpheme.
Thanks to Charles Cairns in comments, I have some example of bound morphemes.
Any prefix or suffix that is not a word in itself is a bound morpheme. That would include terms like infra (used in infrastructure and infrared, but not a word in itself). Also suffixes, like -s and -es to make a word plural. I asked Charles for some word roots that were bound morphemes, and he suggested pant- as in pants and scissor- as in scissors.
Original example, questioned by linguist Charles Cairns in comments.
In contrast, in English, -struct- is a bound morpheme. It is not a word in itself. Yet it can be a suffix, as in instruct, or a prefix, as in structure. Or it can be a root, as in destructive. A unit of meaning that is not
a word in itself, but is any or all of these: prefix, suffix, infix, or root is a bound morpheme.
Charles challenged this because most or all the words that contain -struct- are from the Latin, so it may be that it is a Latin root, but, as new words are not developing in English, not a bound morpheme in English. As he is the expert, I bow to his knowledge. At the same time, I wonder about words like reconstruction, deconstruction, and infrastructure. As I suspect some of these words were created in English, one might make a case for -struct- being a bound morpheme with more and more prefixes and suffixes being added on.
For more, see Bound and unbound morphemes - Wikipedia