What is your question? If you just used the computer but didn't know there was pornography on it, you are not responsible. If you had extended use of the computer, then that might be a different story. Regardless of whether the computer is yours, if you sent and / or received pornography on that computer you can be charged. If you took pornographic photos with the computer, you can be rightfully charged in certain circumstances.
There are several people in Colorado who are qualified computer forensic experts. They can establish when these photos were taken and other information that will point to who owned and operated the computer.
Your public defender should contact them for these services.
Best of luck.
You say you are over 18 therefore your age after 18 does not matter. Mr. Buckley is right a good computer forensics experts can establish a lot in way of proof of whether you knew or should have known of the existence of these type of prohibited photos. Your Public Defender should be able to obtain the expertise from her office. The Colorado Public Defender is a large office with excellent expert resources. If you are unhappy and want to you can always hire private counsel but that will cost you money. You have to look at the investment in your life and future.
Best of Luck
I agree with the other attorneys, however, I suggest that you at least pay for a consultation with a private practice attorney very knowledgeable about sex crimes. Not only are you facing the crime and possible jail, but if you plead you will probably end up on the sex offenders list for life, which could really cramp having a family, kids and a good job. Unfortunately, many public defenders are young and inexperience -- that doesn't mean that they're not good, but it does mean that they don't have all the answers. You should also talk to your PD about having her request co-counsel from the main PD office who is an expert on sex crimes.