You might have seen a dotted rope markup tool in your iOS devices. It is basically a tool by Apple names as Lasso. It allows the user to move the markup on any image they want. It helps in circling, pointing or marking any specific thing in an iDevice on a photo.
If you are thinking where they are located. Then these tools are not hard to find. The markup tools are located in the Editing section of photos app and even the notes app. You can choose them. All you will need to do is select the photos from the Photos app, then you will click on Edit button which is located at upper-right hand corner.
In toolbar, you will see the three dots, there will be an option of Markup, choose it. From this tool, you will be provided by three options of marking up including pencil, pen and highlighter. You will also get lasso tool and an eraser. If you want to change the colour of your markup or writing, simply click on black circle, then select color wheel to select different shades. If you want to choose opacity and tips of writing tool, you will tap the writing tool twice.