So basically spawn vertexes and edges based on ID info stored in a texture pixels? First getting world position of such pixel on a surface of a mesh ?
First you want to store the vertex (and edges ) ID’s in a texture and then using this to make something with that info from that object…
… hmm… why not using the vertex index in the first place… why using the detour via textures… or maybe (easier) using vertex painting to “mark” this ??
Then: there are mutliple examples where people made something on some part of any given geometry… so… i’m wondering about you idea (or the purpose…)…
Next would be: what exactly are you trying… and what did you already tried to make this kind of manipulation… (after a good selection…).
You may have to elaborate this to get a more suited answer.
I just wonder if there might be a way to draw a mesh geometry in a texture someway and make GN create it . For example a stripe of polys with uv based on a curve as input and GN tessellating and displacing it based on texture image . Not like adaptive tesseletion in dx11 displacement but rather explicitly, exactly where I draw it.
Placing specific instance on exact pixel maybe. Not like random probability but rather exactly where red dot in texture is for example? I think I saw something like that in Houdini example and wonder if Blender have some ways to do it .
I may just can’t follow you thoughts…
…or i do not see the benefit… Maybe because i do not know the Houdini example… 
it was a while ago and i don’t have a link . As of benefits it’s might be easier than dealing with index math based selections.
Maybe not by specific color in texture but rather certain uv values? Can i use certain UV value as a position for something in 3d space ?
No… only the other way round… you can look for an 3D space coordinate which 2D UV coordinate they have…
As i said:
Of course you can use any map or vertex color to choose some “behaviour” do be done on any vertex/edge… 
Or… using vertex groups… 