Random image replace from array?

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This is probably not that complicated, but I'm fairly new to JS and can't quite figure out how to do this. I need to have 36 images on a page, their src and link href values pulled from a db with php (I'm fine with that part) and I'd like these images to randomly replace by others. So I'm thinking I need to build a javascript array of say, 72 images, display 36 of them, and then have some kind of random timing where a random image is replaced by the next one in the array. Does this make sense? Is that a reasonable approach?