I create glass etch stencils using both paper stencil material printed using dot matrix printers and thermal stencil material that is printed using desktop thermal label printers. Some of the projects I do consist of simple lines of text and numbers. For this work I have been succesful using MS Publisher. However I am often given “art work” that consists of poor photos of an existing image to replicate. I have no training in graphics arts but have muddled along learning as I go. Sometimes I can make do using MS Paint by importing an image into Paint and cleaning it up enough to create a decent stencil. I am attaching one example of the source material I find myself working with. What you are seeing are essentially negatives. What I am after is the positive version, nicely cleaned up and ready to print on the stencil material. Question? What tools would work best for this work. Ease of learning would help.
I think your best bets would be to purchase Affinnity Photo or subscribe to Adobe’s Creative Cloud to get Photoshop. I am not sure if you can get just Photoshop or if you have to subscribe to the whole suite of software just to get Photoshop. Either way, I’d lean towards purchasing Affinity Photo since it doesn’t sound like you’re in a group workflow. Either one will have a learning curve, but they are substantially better tools than MS Paint. I am not 100% clear on what you’re doing or the end product. If vector art is what you need, look at Affinity Designer or Adobe Illustrator.
GIMP is free and should do what you want.
It sounds like the OP is being given photos of vector art and he’s trying to recreate the vector, maybe?
There are a number of online raster-to-vector generators, with just as many levels of quality amongst them. I don’t use any of them so don’t have any recommendations, but they’re out there.
Sounds like you’re using a paste etch. We usually sandblast or laser etch. With the sandblasting we use either a photo-resist film or, if the design is large enough, a vinyl plotter and paint mask. Sometimes rubber mask but that’s really thick and doesn’t cut well enough for intricate designs.