I gave you a picture of me
and the less grammatically correct but idiomatically common
I gave you a picture of myself
i.e., I gave you a picture of Mari-lou. It is a photo of me/myself, I am in that photo.
Likewise, the phrase I gave Susie a picture of herself means that the photo is of Susie's self; i.e., herself. She is in that photo.
You could say
I gave Susie a picture of Susie.
That works, although repetitive, it is grammatical. Susie is a relatively uncommon name so we would guess that the photo is an image of the same person but it might be that there are two Susies, who can tell? The reflexive pronoun herself removes the ambiguity.
Compare
- I gave Susie a picture of her
Her could refer to Susie or to any woman, by using the reflexive pronoun, herself, we understand specifically who is in the photo.
- I gave Susie a picture of me or myself (a photo of me)
...... /herself (a photo of Susie)
...... /himher (any manwoman)
...... /herhim (any womanman)
...... /us (no ambiguity, it is a photo of Susie and me)
...... /them (two or more people).
Exceptions
In some languages there are verbs that require the reflexive pronoun that are omitted in English. Examples are shave, wash, and dress. In Italian (and I believe in Spanish too) the subject performs these actions on him or herself, thus we have:
radersi to shave (oneself)
mi rado = I shave(myself)
ti radi = you shave (yourself)
si rade = he/she shaves (him/herself)
vi radete = (pl) you shave (yourselves) etc.
lavarsi to wash (oneself)
mi lavo = I wash (myself)
you lavi = you wash (yourself)
si lava = he/she washes (him/herself)
vi lavate = you wash (yourselves)
The British Council website succinctly explains:
NOTE: We do not use a reflexive pronoun after verbs which describe
things people usually do for themselves:
- He washed in cold water.
- He always shaved before going out in the evening.
- Michael dressed and got ready for the party.
We only use reflexives with these verbs for emphasis:
He dressed himself in spite of his injuries.
She’s old enough to wash herself.