About a year ago, when I first started creating products, I tried making the preview collages in Picasa like I had seen online...but I couldn't figure it out. So I resorted to creating the preview in Powerpoint with the jpegs.
I knew there had to be a better way, so I gave Picasa a shot again last weekend. I don't know what was wrong with me a year ago, because this was a piece of cake and took less than a minute to make the collage!
Be forewarned that everything I am going to say is in relation to a Mac...it may be different on a PC, not sure. I don't actually use Picasa for my pictures, so first I had to download the program. You can do that here. The program automatically imported all my pictures after it was installed.
Now, I use iPhoto for my photos, so I'm not exactly sure how it organized those since I don't have them in folders, but it put all my folders of graphics in just like I have them on my computer.
First, you need to save all of your Powerpoint slides as JPEG's. Do this by choosing file, save as, and choose JPEG. A new folder will be created with the pictures inside.
Every time I create a folder of images, it is automatically imported into Picasa.
Select the folder of images you need a collage for and choose create collage.
It does this in seconds! You can change the background color over to the left.
Double tap any of the images to adjust the size, remove them, move them to the back or front, etc. You can also reshuffle down at the bottom in the middle.
If you need to add more pictures from another folder, you can do so after by choosing get more.
When you are satisfied, you need to create the collage.
I think it saves it in Picasa, but I have been choosing file, save as, and saving the image in the folder with the product itself so I have it to upload to TpT.
All done! Super easy!