A controller to reduced power consumption and/or improve outdoor visibility of an organic light emitting display device, and an organic light emitting display device includes the same. The organic light emitting display device including: a light sensor to generate light sensing signals corresponding to an external light intensity; an image judging unit to generate image judging signals, by judging whether images generated by the data signals are moving images or still images; a signal processor to compare the light sensing signals with preset reference values, to generate selection signals, and to modify image data accordingly; a frame memory to store the image data from the signal processor; and a reset signal driver to reset the frame memory according to the image judging signals and the selection signals.