There are a lot of major organisations like Linux, Oracle, Cisco, etc. that offer certification for completing a course. However, there are technologies for which there is no standard certification.
For example, Android programming has no standard certification by any major organisation. There are, however, many private organisations that offer certifications under their own name.
How credible are these certifications when it comes to getting hired?
Personally, I spend time reading books and developing a portfolio than in these certifications because no matter how extensive the course, books generally tend to cover more topics than can be taught in a course.
For example, if I am applying for the job of an Android developer, how credible is a non-standard cert as a proof of knowledge?