So i try to add category instead keywords but could not figure it out. Anyone know how to do this?
This dosn't make sense, I think. Based on categories
all images of the same category are similar. Self-evident, isn't it? To do so, you simply can use the categories template tags.
Mod similar images does not complex analysis of image description or keywords, it just uses php-own string comparison. So the results strongly depends on the quality of your metadata. If you don't use controlled vocabulary and consistent structure or systematic, results will be unsatisfying. For my experience only less galery operators pay attention to metadata, but metadata are the key to any information processing. To get proper results with this mod, set up your image description and keywords with controlled vocabulary and consistent structure first. This can be very time-expensive, but there's no other way.