Regardless of where you are uploading your photo in thanks.io, you should prepare it ahead of time.
If you are not familiar with photo-techno-babble then please do not hesitate to send the photo you want to use to us, and we'll take care of it. All you need to do is click on the chat icon on the bottom right corner of your screen, and start a conversation. You'll see an icon to attach the photo you want us to work on. Be sure to include a message to say 'Hi!'
DIY Photo Dimensions
To ensure your photo fits on your postcard please make sure you have the photo sized to 1875 x 1275 pixels, and for best print quality, 300 DPI. The file must not exceed 10MB. You can download a PSD file which contains the cut and safety boundaries for the edge of the card, here.