An electronic device comprising: a first image sensor of a low capacity located in a front of the electronic device configured to generate low-capacity image data; a second image sensor of a high capacity located in a rear of the electronic device configured to generate high-capacity image data; a display unit configured to display an image; and one or more processors (310, 340) configured to: generate a first preview image by using only the low-capacity image data; display the first preview image on the display unit; and convert the high-capacity image data into a preview format to generate a second preview image of the high-capacity image data; in response to an occurrence of a capture event, wherein when the capture event takes place by a time of a processing delay of the high-capacity image data, recognize and synthesize as capture image data the low-capacity image data corresponding to the first preview image data displayed on the display unit at a capture event occurrence time point and the high-capacity image data including an image acquisition time stamp corresponding to the capture event occurrence time point, and generate thumbnail data using the low-capacity image data and the high-capacity image data by synthesising first preview image data displayed on the display unit at the capture event occurrence time point and the second preview image data including the image acquisition time stamp corresponding to the capture event occurrence time point. a first image sensor of a low capacity located in a front of the electronic device configured to generate low-capacity image data; a second image sensor of a high capacity located in a rear of the electronic device configured to generate high-capacity image data; a display unit configured to display an image; and one or more processors (310, 340) configured to: generate a first preview image by using only the low-capacity image data; display the first preview image on the display unit; and convert the high-capacity image data into a preview format to generate a second preview image of the high-capacity image data; in response to an occurrence of a capture event, wherein when the capture event takes place by a time of a processing delay of the high-capacity image data, recognize and synthesize as capture image data the low-capacity image data corresponding to the first preview image data displayed on the display unit at a capture event occurrence time point and the high-capacity image data including an image acquisition time stamp corresponding to the capture event occurrence time point, and generate thumbnail data using the low-capacity image data and the high-capacity image data by synthesising first preview image data displayed on the display unit at the capture event occurrence time point and the second preview image data including the image acquisition time stamp corresponding to the capture event occurrence time point. generate a first preview image by using only the low-capacity image data; display the first preview image on the display unit; and convert the high-capacity image data into a preview format to generate a second preview image of the high-capacity image data; in response to an occurrence of a capture event, wherein when the capture event takes place by a time of a processing delay of the high-capacity image data, recognize and synthesize as capture image data the low-capacity image data corresponding to the first preview image data displayed on the display unit at a capture event occurrence time point and the high-capacity image data including an image acquisition time stamp corresponding to the capture event occurrence time point, and generate thumbnail data using the low-capacity image data and the high-capacity image data by synthesising first preview image data displayed on the display unit at the capture event occurrence time point and the second preview image data including the image acquisition time stamp corresponding to the capture event occurrence time point.