While Apple’s Photos app is a handy way to organize your photos, its options for converting and updating metadata are limited at best, so in these cases you’re better off simply exporting your photos and passing them through a third-party app more specifically geared toward the task. Enter Overmacs’ Reformator ($12), an app expressly designed for bulk image operations, including converting into popular formats, assigning meaningful names, watermarking with text and images, making adjustments, and more.
Feed a batch of photos into Reformator, and you can group and browse through them using a variety of crtieria ranging from capture dates to resolution and color profiles. You can then select a set of photos and carry out a series of actions on them — convert them to different formats, color models, or color depths, correct EXIF and IPTC metadata, add GPS coordinates, remove private metadata, add copyright, keywords, and rating, rename them using any metadata available, crop, scale, add borders, change resolution, and even add a watermark with text or images. The app even lets you configure presets to quickly setup a workflow using the same set of actions, and provides some examples to get you started, such as preparing photos to upload to Facebook or watermarking with the photo’s capture date.