Why would I need to resize the images?
Images with different aspect ratios may skew how your images compare against each other.
What is an image canvas?
Like a picture in a picture frame, the canvas of an image is what the image is on top of. In almost all cases, the image canvas is exactly the same size as the image. However, you can adjust the image canvas to be larger than the image if you want the image to have a particular size. The extra space is essentially blank padding.
Steps to resize your image canvas
1. Go to the Pixlr Editor website and launch the Pixlr X free edition (if you don't have an account).
2. Select Open Image from the bottom left of the screen and upload the photo you wish to resize.
3. Click on Layout & Template.
4. Select Canvas Re-size.
5. Change the anchor point for the current image and choose your final canvas size. Try to either make the smallest of your images match the width of your largest image or adjust them all to be the same canvas size. Hit Apply once done to see and save changes.
Note: The anchor point is where the current image will be set, and the additional size will be added around that point.
4. Save the file. Now you can upload the image back to PickFu.
Here's a video for more explanation.