I've screwed around with photoshop on and off for years. I'm not a professional by any means but there's plenty of stuff I do know how to do.
Sometimes simply editing a photo doesn't do exactly what you're after and in terms of clip art style images you usually have to redraw them in illustrator to make them vector images so they don't look to grainy.
Actual photos it helps to have multiple shots from the same angle. When you only have one photo to work with you're a little more limited on what you can do with out a ton of work but it's still manageable.
With what you provided you could select out the middle banner, make it it's own layer and then adjust the transparency of it but it would bleed into the background layer of the country with the flag superimposed on it. You could leave it solid and adjust the background layer transparency to make it stand out more. You could apply a clipping mask to the top banner to make it blend into the background layer. Or just outright adjust the transparency of the whole image.
