From the Store description:
A picture is worth a thousand words. Following this motto, Photo Marker allows you to take notes on your photos, so that you can make it more expressive. Mark words of a scanned or photographed text, easily explain the way on a map or highlight and share the things that are important for you. Using Photo Marker, these tasks are going to be very easy!
In addition, the app allows you to insert text or various kinds of shapes. Using pinch-to-zoom and panning, everything becomes fast and very easy.
Especially welcome, if not evident here in the screenshots, is that the full original image resolution is maintained, so you don't lose image quality in the annotating process - other than your own scribbles, of course. Related to this, I was impressed that the photo picker that Photo Marker opens with also allows the opening of previously annotated saved images - again, because the original resolution is maintained, you can think of these as saved Photo Marker 'projects'.
Here's the application in use, with comments:
The main interface, a dense but powerful set of colour, opacity and thickness controls, for freehand notes, arrows, lines, circles, and so on; (right) plus a text mode, in which anything you type can be positioned on the image wherever you like, desktop-publishing-style. With multi-touch pan and zoom, you can work on any part of the image and move it around to your heart's content.
Seen here on this thumbnail of a previously 'marked' photo, some free hand text, which is another option, depending on your creative you are; (right) if you do choose machine text, there's a long list of fonts, sizes and emphases to pick from.
The free version has a few subtle limits - the main one is not being able to include multiple text elements (i.e. paras) - you'll need to upgrade if you want to get ambitious, which is fair enough! (right) annotating another photo, this time using the 'arrow' tool....
Baked into the editing interface is a cropper and, shown here, an EXIF viewer, which is handy - the data presented goes way beyond the screenshot here and scrolls for several panes....
Although on my radar to review for a while, I never felt Photo Marker was 'there' in terms of its potential. With the latest update, a couple of days ago, it's now polished and professional. And, in more skilled hands than mine, could well offer potential for some useful effects and notes, before passing photos on to others.