With summer heating up, camera-phone usage has soared in the U.S., according to M:Metrics, a Seattle-based research firm.

M:Metrics said photo messaging has increased 32 percent since February.

Also since February, the number of camera phones in France, Germany, the U.K. and the U.S. has grown 22 percent, to slightly more than half of all cellphone owners.

That increase in ownership and the quality of cameras are leading reasons why people are snapping more pics, said Mark Donovan, M:Metric's vice president and senior analyst.

"We also see a direct correlation between camera resolution and propensity to use photo messaging, as 44.3 percent of subscribers who own phones with cameras with resolutions exceeding one mega-pixel sent a photo over the network, versus a global average of 30.5 percent," Donovan said.

The statistics came out in connection with M:Metric's June study that details a number of wireless trends.