在车上拍照的英文表达是 "take photos while on the train/vehicle"。这种表达源自英语中常见的结构 "verb while doing something else"，例如：

"I'll send you a message while I'm on the train." (我坐火车的时候会给你发信息。)
"I pke to read while I'm waiting for the train." (我喜欢在等火车的时候看书。)

如果你想要表达的是下车拍照的意思，可以使用 "take photos after getting off the train/vehicle"。例如：

"We'll take photos after getting off the train at the next station." (我们会在下一站下车后拍照。)
"We planned to take photos of the beautiful countryside after getting off the bus." (我们计划在下车后拍摄美丽的乡村风光。)