Yes, and InmateAid is built exactly for this situation. You write the letter online through the InmateAid website, upload any photos you want to include, and InmateAid handles all the printing and mailing from their office in Florida. Because the office is already in Florida, the letter typically reaches the facility within one day of being sent, far faster than anything mailed internationally from the UK.
This means you never have to worry about international postage, customs delays, or the logistics of sending physical mail across the Atlantic. You write it from your phone or computer, InmateAid prints and mails it locally, and your person receives it through the facility's normal mail process.
To get started, create an account on InmateAid, add the inmate's details, including their name, ID number, and facility, and then use the letter service to compose and send your first letter. The return address on the envelope will be InmateAid's Florida office rather than your UK address, which also keeps your personal information private.