The photo is of Ira's son. Photography was in its infancy when this Ira died. This biography written by someone else also has some dates incorrect. John visited WI in 1847 and talked his brother, Ira, into going back east to Vermont and joining the US Army to fight in the Mexican-American War. They enlisted at Burlington, VT on 1 May 1847 and left almost immediately for Mexico. They were in a large group of soldiers who contracted disease caused by the water supply. The able-bodied moved on and left the rest of them in a hospital in Puebla, Puebla, Mexico where most of them eventually died and were buried in a large trench dug along side the hospital.

Ancestry.com. U.S. Army, Register of Enlistments, 1798-1914 [database on-line]. Provo, UT, USA: Ancestry.com Operations Inc, 2007.
Original data: Register of Enlistments in the U.S. Army, 1798-1914; (National Archives Microfilm Publication M233, 81 rolls); Records of the Adjutant General's Office, 1780's-1917, Record Group 94; National Archives, Washington, D.C.
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Ancestry.com
US Army Register of Enlistments: 1798-1914

1847 Jan- 1849 Jun Mexican War

Image 32/541-both enlisted 1 May 1847 Burlington, VT..Assigned 7th Div
.both died 6 Oct 1847 at Puebla, Mexico

Eyes Hair Complex. Height Occupation
Blackmer Ira R. Blue Brown Fair 5' 10" b. Dana, MA Farmer
Blackmer John S. Brown Black Hardy 5' 8" b. Rutland, VT Farmer
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Cerro Gordo and Puebla

Almost immediately Scott began the advance toward Mexico City. Only sporadic resistance was encountered until his army reached the village of Cerro Gordo about 80 km (50 mi) inland. There, in a narrow defile, Santa Anna prepared to turn back the Americans. The attack on Cerro Gordo was led by units under William J. Worth on April 18. The U.S. engineers, who included Robert E. Lee, George B. McClellan, Joseph E. Johnston, and P. G. T. Beauregard, found a trail that enabled the Americans to envelop and rout Santa Anna's forces. The Mexicans lost 1,000 men in casualties and another 3,000 as prisoners. The Americans had 64 killed and 353 wounded.

Pursuit was impossible, but Worth moved up the road to occupy the venerable Perote Castle on April 22. Scott and the main army had entered Jalapa on April 19. There the advance stopped for a month. Scott reported over 1,000 men bedridden in Veracruz and another 1,000 sick at Jalapa.

On May 14-15, Worth and John A. Quitman moved into Puebla, about 80 km (50 mi) closer to Mexico City. They expected heavy resistance because of Santa Anna's reported presence there. However, the town's leaders and the priests had decided to open Puebla to the Americans. Santa Anna had only about 2,000 cavalry, which the Americans easily routed. Another 1,000 Americans fell sick at Puebla, apparently from the local water supply. By July 15, with recent augmentations, Scott's forces numbered about 14,000. However, over 3,000 were sick or convalescent, and the sickness rate showed no sign of decreasing.
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Bibliography:

Bauer, K. Jack, The Mexican War (1974); Bill, Alfred H., Rehearsal for Conflict: The War with Mexico, 1846-1848 (1945; repr. 1970); Connor, Seymour V., and Faulk, Odie B., North America Divided: The Mexican War, 1846-1848 (1971); Dufour, Charles L., The Mexican War: A Compact History (1968); Eisenhower, John S. D., So Far from God: The U. S. War with Mexico, 1846-48 (1989; repr. 1990); Johannsen, R. W., To the Halls of the Montezumas: The Mexican War in the American Imagination (1985; repr. 1988); Nichols, Edward J., Zach Taylor's Little Army (1963); Ruiz, Ramon E., ed., Mexican War (1963); Schroeder, J. H., Mr. Polk's War (1974); Singletary, Otis A., Mexican War (1960); Smith, Justin H., War with Mexico, 2 vols. (1919; repr. 1963); Weems, J. E., To Conquer a Peace (1988)

For more information, look at the Descendants of Mexican War Veterans site.
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Ancestry.com
US Army Register of Enlistments: 1798-1914