How do I Randomise images and then have half of those images shown again in a different block?

Hello,
I'm currently working on a research study whereby participants are shown images one at a time for 3secs from 3 different image categories (10 pictures from each category). These images are shown in a randomised order and from a selection of 30 pictures in each category. After each image is shown, participants then answer a question on a separate follow-up screen asking how bright/how much the image moves them. This order is repeated so participants see an image, answer the question, see the image then answer the question, and so on.
After this, we want participants to then in a different block see half of the images from each category randomly shown again along with images they haven't been seen before and then rate each image as new or old. This order will be the same as before as in an image will be shown followed by the question (is it new/old) and will repeat.
The problem we are having is how to randomise the pictures in terms of categories so a certain number of each is select in one block. Along with this, we are unsure on how to show the same images participants were shown again in a different block but only half of them images, again split in categories (5 images from each of the 3 categories).
Is there loop and merge/randomisation/javascript we can use to do this? We have been able to find javascripts for showing the images at 3s each time but not a way to display a certain amount of images from each group in one block followed by half of the same images shown again coupled with new images/images not shown before
 
Any help would be massively appreciated!
 
Thank you!