Click in browser button and then add a source PDF to sign and an image to insert into PDF. In the options you can set size and position of image within PDF
Through API you can sign a PDF with an image using JSON or POST call. PHP, Java, Ruby, Python, .NET and more support these types of calls. API
The web app is browser-based. So, it works for all operating systems including Mac, Windows, and Linux.
You can select the position through coordinates. Size is set to real millimeters. In this way, if, for example, the page size is A4, you could set the size and position of the image based on the size of that page.