Updated: Oct 4
Save an image as a PSD, then break it up into layers. I took this pic recently and divided it up in to three: the sky, the lake (and horizon) and the foreground.
I selected the sky with the Quick Selection tool in Photoshop and copied it to a new layer with 'cmnd . cntrl + J'. The 'lake' layer had the nice horizon at the top, and a fuzzy edge caused by me and the eraser tool. This was because wanted it to fade into the foreground layer, where I intended to apply some 'windy day' effects.
In After Effects I imported the saved PSD and made sure that 'Composition - Retain layer sizes' was selected as the 'import kind'. Then I double-clicked on the Composition icon, just below the images in the Project panel, which opened them all as layers in the Timeline. Doing this automatically created a Composition, which was fine, but I wanted to set the duration of it myself. So I opened up the Comp Settings panel and entered '0;00;10;00' as the duration.
The image layers weren't in quite the right order for what I wanted, so I dragged the 'lake' up to the top of the stack. This would then create a clean horizon, and mask the edge of the effects I intended to apply to the foreground.
I searched for the 'CC Slide' effect in AE and dragged it on to the sky layer. Slide has a 'floor'point, which remains fairly static, but further away from it the image is more strongly affected. So I put the 'floor' point near the horizon of the sky layer, leaving the upper part to swoosh along as if a strong wind was blowing it.
Because 'Slide' sways the image from one side to the other I needed to scale up the sky to 150%. This wasn't keyframed, as I wanted the scale effect to be there for the whole sequence.
I put the Playhead at the start of the Timeline and dragged the 'slide' setting to the left until I could see a black area appearing in the top right corner of the image. That meant I'd just run out of sky! I backed off until the black area closed up, and keyframed the setting. Then I dragged the Playhead all the way to the end and dragged the setting to the right. I now had slide settings from -70, at the start, to +70 at the end.
On the ‘lake’ layer I ran the eraser along the bottom edge, to feather it a bit. But I didn't need to add any effects to it.
I selected the foreground, searched for the ‘ripple’ effect and dragged it on to the layer. To look like a gentle breeze ruffling the grass and flowers it needed to be quite subtle. But it also needed to stretch right across the image. So, I duplicated it. One was positioned to the left of the vertical centre of the image, and one just to the right. I used the same settings on both: A radius of 75, wave speed of 0.5, wave width of 2 and wave height of 4. The ripple phase doesn't really affect it in this case, so I left it unchanged.
I played the movie a couple of times, then chose 'File > Export > Queue in Adobe Media Encoder'. And the result is...here.