CENTER CITY (WPVI) -- Philadelphia police have released surveillance pictures of two men they believe placed skimming devices on automated teller machines (ATMs) at a Center City gas station.Investigators say the devices were installed on September 14th and 15th at the Sunoco gas station at 22nd and Walnut streets.Police believe the suspects may be traveling between New York and Philadelphia.ATM skimmers are devices that read the data off of a card's magnetic strip.Anyone with who recognizes either man is asked to contact the Philadelphia Police Major Crimes Unit at 215-686-3396/3397, or call 911.Police have not commented on how many customers may have been affected by the device.