For whom he did foreknow, he also did predestinate to be conformed to the image of his Son....  (Romans 8:29)

Predestination addresses only believers as to their future state.  Romans 8:29 speaks of believers in their future glorified state.  At the moment of salvation, each child of God is predestined to be "conformed to the image" of Christ.  It is no longer an option - but a certainty.

The "image" of the Son speaks of both resembling Christ and representing Him.  We will not represent something like Him, "but rather what He is in Himself--both in His spiritual body and in His moral character."  (W.E. Vine, M.A.).  "And as we have borne the image of the earthy, we shall also bear the image of the heavenly." (I Cor. 15:49).   See also Philippians 3:21.

Salvation has delivered us from the penalty of sin once for all (Romans 8:1).  Sanctification is now saving us from the power of sin (Romans 6:22).  At the Day of Christ,  glorification will render us free from the very presence of sin (Romans 8:18-25).

Beloved, now are we the children of God, and it doth not yet appear what we shall be, but we know that, when he shall appear, we shall be like him....  (I John 3:2).

[Scripture is from the New Scofield Reference Bible, Oxford University Press, 1967].