Interpretation of adding some graffiti.

[crabtrem]

Here is a novice's interpretation of placing some graffiti on a wall. 

I start with two images I want to combine. A background image with a wall. And the other item I want to place on the wall. I used an image, the Affinity guys have already made a great tutorial covering text. Actually there are 2 different one's I believe.

So I start with my image and make a selection of the area I want to bring over, save it to a new layer.

I posterize that selection to make it look more like a painted image.

I copy that selection, and paste it into my wall image. 

Selecting the pasted image I set the blend mode to something that works, in this case vivid light at 100% opacity worked best for me. I selected the pasted section and choose the perspective tool to adjust the proportions of the image to match the wall. Now I select the mask portion of the pasted image, select a brush that will allow me to rough up the image. I chose the Painting brush 64 in this case and reduced opacity, flow, and hardness down a bit. I then rough up the edges and mottle the painting to reproduce some weathering. 

Next I make a copy of the pasted image layer, I add the fx color overlay and select a color that I think best represents overall reflected light. I choose the blend mode to color, and then reduce the opacity.

And that's it. Hopefully you will find something useful in this interpretation from a novice. Cheers.