Pickerel Frogs (Lithobates palustris) are spotted amphibians found throughout New England. They're recognized visually by their dark squarish spots on light brown bodies. Two rows of spots usually cover their backs, but, as this Pickerel Frog shows, sometimes the spots merge to form rectangular patches. They can also be recognized by ear: listen for the snore-like calls of males from wetlands in spring (listen to this sample).
These three photos are of a Pickerel Frog I encountered near the parking area of the Eagle Scout Nature Trail in Plainville, MA on 9/24/12.