Plastic surgeon or a dermatologic surgeon for tattoo excision?

Without seeing pictures or seeing you in person it is impossible to give you specific advice.  However a 2.5 x 1 inch tattoo over the rib cage is generally amenable to excision.  We also offer PICO laser for laser tattoo removal 

While any doctor could physically do this procedure plastic surgeons are typically the ones who perform cosmetic excisions such as this.  Some dermatologists certainly may offer this and certainly may do an excellent job excising a tattoo.  At the end of the day it is all about who you are comfortable having do this.  Good luck!