You can use below CSS override code, to use the store image as backround-size CSS Style Contain instead of Cover.

.ssf-main-content .info-img { 
  background-size : contain !important; 
  background-position: 50% 50% !important; 
}

For standalone version, using Mega Locator theme, you can edit css/mega-superstorefinder.css and paste below code at the very bottom of the file.

.info-img { 
  background-size : contain !important; 
  background-position: 50% 50% !important; 
}