Corrected entry: How did the FBI get the photo of Michael's tattoo? Michael would not have wanted anyone to have a photo of it in case they figured out his plan, and also the only photo they would take for prison would be a mugshot of his head.
Correction: The tattoo artist tells the agents when interviewed that Michael was incredibly specific and designed the whole thing himself, which would have been a difficult task for a tattoo artist, having not worked on any preliminary sketches. This, coupled with the fact that a tattoo artist's portfolio is made of photos of their work, would mean that the artist would most certainly take detailed pictures. This is standard practice for custom work, and anything large or intricate. If Michael had refused, he may have alerted suspicion, and it also may have been an agreement with the artist that they would only do the work if it could go in their portfolio. Plus photographs of tattoos are taken as part of the identification process during various stages of being incarcerated. The FBI could have gotten the photographs from any number of sources within Department of Corrections or Chicago Police.
Correction: When being admitted to prison they will have taken detailed photos of his tattoos for their records under the distinctive tattoos section so if they did escape they would be able to compare his tattoos to those on file to make sure they got the right man. The FBI had age as to his prison record. So they got it from there.
Ssiscool ★