Following a suggestion from Moonlight Reader, I thought I'd compile a list of online photo editing sites that players can use to mark their cards since Picmonkey no longer has free accounts. Which I rather rudely found out in the middle of Halloween Bingo last year. It's a shame because I really liked Picmonkey. I believe that MR uses the site to make our absolutely gorgeous bingo cards.
I've not been able to find anything I liked quite as much, but here are a few options. Note: outside of the first one, I've not tried any of these. I've only checked to see that they offer a free option and have stickers that are Halloween/Autumn related.
BeFunky - This is the one I settled on after I had to stop using Picmonkey. It's easy to use and has a nice selection of stickers. You can also upload your own graphics to use as stickers. There are free and paid versions. I used a combination of Halloween and Autumn stickers to mark my card last year. Not sure if I'll use the same stickers or choose new ones. Or try one of these other options.
Ribbet - Has free and paid accounts. There's a small selection of Halloween stickers. This one seems to save a copy of the last thing you edited even without an account. I signed up for a free account and it says I can now upload 100 photos.
Fotojet - Has free and paid accounts. There is a small selection of Halloween stickers.
Fotor - Has free and paid accounts. Has a nice selection of Halloween stickers. You can also upload your own images to use as stickers.
Pixlr Express - Free. Doesn't have a Halloween sticker section that I can see, but a few stickers out of some of the other categories would work.
If anyone has more suggestions, please let me know in the comments and I'll edit them in.