How to link Images of one node to other node?
Whichever way you look at it I would say that these images should be a field on the entity that they are linking to ( you are going to have a validation nightmare having a multiple image field and an entity reference field that can't be forced to have x number of values easily ). The easiest way to then render these would be to use the views module, create a block displaying fields and selecting he image field and clicking the box to link the image to the original piece of content. You can also have a filter to select only entities where this field is filled.

In reality though a better approach would be to create a menu ( this is what you are doing after all ) and put in the images using css.
example:

#block-system-main-menu li a {
  display:block;
  width:100px;
  height:100px;
  background-repeat:no-repeat;
}
#block-system-main-menu li:nth-child(1) a {
  background-image:url('../images/icon_1.png');
}
#block-system-main-menu li:nth-child(2) a {
  background-image:url('../images/icon_2.png');
}