I love sketch effects in layouts. The style is popping up all over the place, it seems like. It's easy to achieve, often just a quick menu item in image editing software. I used a sketch effect in Pixelmator and overlaid it on the photo with blending modes selected for
Tardenois, above.
More blending and sketch effects in Pixelmator, for
happy, below. I left some of the sketch-only pieces visible just at the top of the leaves, and also at the bottom left. By positioning blended, sketched layers one on top of another, it almost gives the leaves a 3D look. For the heart, I stamped the cool image on the page, hand-drew a heart shape, created a selection, then applied a mask to the layer.
Moment Captured, below. More sketch effects, as well as some color hatch effects, plus a bit of colorization and masking. Also done in Pixelmator.
Wendyzine has a terrific Photoshop
sketch action. I did this page using her action, some photo masks and blending / layering in Photoshop.