They have no name associated with this portrait they just think it is Shakespeare, someone had once scribbled “Sir Walter Raleigh” on the back but it doesn’t resemble him. This portrait has been copied several times, but again without the copies being identified as Shakespeare. So ....
Looks like the Earl of Oxford to me.
Shakespeare’s plays weren’t sold (legally) in his lifetime. Bootleggers transcribed the scripts from the audience. It wasn’t until after his death that proper editions started to come out.
They compared it to engravings of Shakespeare published after his death, and when superimposed, the engravings look like this portrait was used as the model.