I found this info on the Russian site. (using chrome and being translated from Russian, so there might be grammar and other problems)
Scans (photo cards and stickers)
Technical requirements for scans:
1. The picture size on the larger side for the labels is
600px , for the cards -
800px . Updated!
2. The format is JPG.
3. The file name must strictly correspond to the number of the label.
Example 123.jpg (sticker number 123),
v10.jpg (sticker number V10, lowercase lettering must be)
4. The sticker must be cut evenly, without page background.
5. Only
quality images are accepted . It is highly desirable that the cards and stickers be scanned, not photographed.
Detailed
requirements for the quality of images (scans, photos)
Send scans to the mailbox: content@laststicker.ru
Mail is parsed in the order of the queue, so the addition may take some time. To notify additionally through personal messages to the administration of the site that you did not need to send the letter.
Did you get any reply from them btw ?