You may have checked the "exclude unused files" option when deploying. This means only the images you've used on events or set up in the database will be included, and those used purely by plugins and nothing else will not be. There is a way for plugin authors to specify that the files they use should be included when that option is checked, but it's a bit messy and to my knowledge, most don't do it.
So you can either deploy without checking that option, which will give you a very large file because the entire RTP will be included whether you use it or not, or you can deploy with that option, then go through all your plugins and see what resources they use, and copy them over into your deploy folder. The other option is to go through and remove all RTP resources that you're not using, then deploy without checking that option. That's usually easier when you do it right at the start of a project though, and add in the files you need, as you need them.