The Collaborative International Dictionary of English v.0.48:

Im- \Im-\
   A form of the prefix in- not, and in- in. See In-. Im- also
   occurs in composition with some words not of Latin origin;
   as, imbank, imbitter.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

I'm \I'm\
   A contraction of I am.
   [1913 Webster]