The key word here is work. I find that many are unwilling to invest the time. Even so here's how I'd approach this.
1. Read https://forums.getpaint.net/topic/22231-transparent-letters/
OK, now we have a layer with the text showing what's underneath. Now we need a Mosaic to go under this transparent text.
2. We'll use a Mosaic app (too many to pick one for you) so you create a big mosaic then put that on the layer your transparent text will be on top of.
3. Working with layers: https://www.google.com/search?q=layers+in+Paint.net&gl=US
I want to merge multiple pictures to create letters, for example I want to take about 75 pictures and collage them to create the words "thanks Coach" with each letter being its own 4x6 photo
Does anyone know how to do this or an app that could help me? I cannot find an app that will allow me to do this.