This isn’t an issue but I couldn’t find an answer.
I like to use another programs (Photoshop or Sketchbook) to draw the background for my scenes then import them to Harmony. What I don’t like is the fact that I have to make a new layer every time I insert an image. I would like for them to be on one layer like my cel drawings
You could group them. Or is there some reason you don’t like it that way?
Maybe I don’t understand your question. Background images for most cases will fill the whole scene exposure and be on their own layer - for instance, on layer for the sky, another for the mountains, another for the foreground. In which situations would you want several background images on the same layer? If you would want some sort of animation or change on the background, I assume. In any case, if you want to import a file from Photoshop - or whatever software that can save a PSD file, I suppose - if you create a group with several layers, when importing the PSD file to Harmony you will get a layer with the name of the group with all the Photoshop layers on the same Harmony layer.
You can also choose the option to add and image to an existing layer instead of creating a new layer.