While most European countries have settled into standard for passport photos, the Irish are close, but not quite ready to square up with their Euro-brethren.
The Irish passport photo's stated required size is 35-38mm wide by 45-50mm tall (nearly all European photos are 35x45mm). A white or light colored background (compared to only light gray for the UK, France, or Germany), and although you may submit color, they prefer black and white (nearly all countries require color only).
To their credit, a handy overlay is supplied by Ireland to make sure your image will conform to their size standards.
If you want to be sure your Irish passport photos will pass muster, contact Newsome's Studio of Photography at 813-968-2810. Located at 10012 N. Dale Mabry Hwy, Suite 219 in Carrollwood (behind Starbucks at the corner of Linebaugh Ave and North Dale Mabry Hwy, just north of Busch Blvd).