In Othello what was Shakespeare trying to achieve through his use of Imagery? Specifically that of Hell/Demons, Sight/Blindness, and Animals.
You have several questions embedded here. I can address the animal imagery. It is Iago who first makes use of animal imagery. He calls Othello "an ass." When he and Roderigo tell Brabantio of Othello's elopement with Desdemona, Iago calls Othello a "black ram" who is "tuppng your white ewe." Later he describes the consummation of the marriage as "making the beast with two backs." This imagery is clearly disparaging, and it is imagery that Iago applies to many characters, including Roderigo, whom he later refers to as a "snipe." This shows Iago's sense of superiority and his lack of respect for others.
What is interesting, though, is that as various characters fall under Iago's influence, they begin to use animal imagery as well. Cassio, after becoming drunk and engaging in a fight with Montano, declares that he has become "bestial." Othello later beings to echo Iago as iterates "goats and monkeys" when he thinks of Desdemona and Cassio together. Even Roderigo describes himself as a "hound."
It is not until Act 5 that a character, though, finally labels Iago as less than human. Surprisingly, this character is Roderigo. In his last words, Roderigo calls Iago " a damned inhuman dog." Of course, this epiphany is a little too late. The damage has been done.