Certain embodiments involve blending images using neural networks to automatically generate alignment or photometric adjustments that control image blending operations. For instance, a foreground image and a background image data are provided to an adjustment-prediction network that has been trained, using a reward network, to compute alignment or photometric adjustments that optimize blending reward scores. An adjustment action (e.g., an alignment or photometric adjustment) is computed by applying the adjustment-prediction network to the foreground image and the background image data. A target background region is extracted from the background image data by applying the adjustment action to the background image data. The target background region is blended with the foreground image, and the resultant blended image is outputted.