It depends on the facility and who is processing the mail that day, which is not the most satisfying answer but it is the honest one.
Most facilities use the inmate ID number to match incoming mail to the correct person, particularly at larger institutions where multiple inmates may share similar names. Without that number, the mailroom has to rely solely on the full legal name to make the match. At smaller facilities with manageable populations, that works fine. At larger prisons with hundreds or thousands of inmates, a missing ID number increases the chance that mail gets held, returned, or misdelivered.
The safest practice is always to include the full legal name exactly as it appears in the facility's system along with the inmate ID number on every piece of mail. That combination removes any ambiguity on the mailroom end and gives your letter and photos the best chance of arriving without delay.
If you have already sent something through InmateAid without the ID number and it comes back, do not worry about it. InmateAid will fix the error and resend everything at no charge. Just email aid@inmateaid.com, let the team know what happened, and provide the correct ID number so the resend goes out with complete information.
Going forward, take a moment to confirm your inmate's ID number before placing any order. It is typically found on any court documents, facility correspondence, or through the relevant inmate locator database for the system he is in. Adding it to your InmateAid account profile now means you will not have to look it up each time.