In case someone finds this useful:
I use LogoLicious in android to add watermarks from my cellphone. It allows me to keep the original size of the image, which Watermark didn't (the screenshots looked really tiny and awful when I uploaded them). I just leave it here in case someone has the same problem as me with Watermark.
i have a account with Solomon clear and this servants: https://photos.google.com/share/AF1QipNkxPwug3KFxM3FalTmn3GZSkY2eofp93leqz3UzQRcuVxi2Mj7FmFtZKYMpOeKng/photo/AF1QipPWZh3w1ICQO66guY2AcfJ8ylLeJbZMRmWzy03n?key=Q1A4R096UmpleThWVmhJVTVoMUVBRVJzMGgyMmVR