1. First, find a picture of an object you want to add condensation to. All black, or all white objects don't work as well.
2. Next, create a new layer. Go to Edit> Fill>... next to Use: select 50% Gray.
3. Filter> Render> Fibers
4. Filter> Blur> Gaussian Blur. Move the slider down so it just gives it a slight blur.
5. Filter> Texture> Stained Glass. Adjust the 'Cell Size' and 'Border Thickness' to get what looks like angled bubbles that are close to the size you want.
6. Filter> Sketch> Plaster. This will round off the bubbles. Adjust the sliders to increase or decrease the amount of bubbles. Don't worry about selecting too many. You can use the Eraser tool later to get rid of some.
7. Using the Magic Wand tool with the Contiguous box checked, select and delete the black around the bubbles.
8. Go to Edit and select Free Transform. Right-click inside the image and select Warp. Move the sides in to follow the curves of your object. Don't worry about any that are left outside of it.
9. With your bubbles layer still selected, go to the Layers palette. In the dropdown box select Overlay. Your bubbles inside the image will become more realistic, and the ones outside will disappear.
10. Before and after.
