Sending thank you cards after Christmas is a bore, and in this digital age sometimes it can even feel like too much effort to go to the post office. Well, now there's an app for this too.

Inkly is an Android and iOS app that lets users choose physical greeting cards they want to send to friends and loved ones. You don't need to print the cards out – all you have to do is pick a card template from more than 3,500 designs in the app (including ones from well-known US and UK greeting card brands stocked in high street gift shops), customise it with your own photos if you wish, and then write your message on a piece of paper and let the app scan it.

Using a sophisticated image-processing algorithm, the app takes a photo of your handwritten message and then analyses the entire image pixel-by-pixel, to detect what is handwriting and what isn't to remove the background completely.

Inkly then prints out the card, which looks like you've handwritten your message, and then posts it for you.

"We're mobile first — everything is done through the app," Inkly co-founder Lee Hawkins told IBTimes UK. "We're trying to bridge the gap between the convenience of digital and online, which we all love now and have got used to, while still trying to keep that personal touch. When you receive a card from someone, when you see the handwritten message, you feel a connection to that person.

"Everything used to be sent through the post," said Hawkins. "Then email came along and the use of post became less and less, and now there's social media, so almost no letters are sent. Receiving something in the mail is different, it's a lot more meaningful and heartfelt."

The Inkly app has now had more than 400,000 downloads on both the iOS and Android app stores. Birthday cards are the most popular product on the service and of course Christmas is a busy time too, but the London-based firm has noticed a huge amount of interest in postcards too, which are cheaper to send and feature a photo of the user's choosing as the main image on the single-sided card.

"Traditionally people buy postcards when they're on holiday and send them when they get home. Nowadays we're finding people seem to be sending digital postcards all the time – whether they're at the park or at someone's birthday party, they just use the photos on their phones and then add a handwritten or typed message on the back," said Hawkins.

People who receive a card can also keep a digital version of the card by downloading the Inkly app and then scanning a unique barcode printed on the back of the card. And they can also instantly send a digital "thank you" to the sender through the app.

Inkly charges £2.99 for each greeting card sent (plus £0.62 postage) and 99p for each postcard (plus £0.62 postage).

The service was first launched in the UK in 2015 and recently made its debut in the US over the holiday season, with a special promotion offering all T-Mobile customers a free Christmas card.

The app developer prints the cards locally in each location and plans to next set up a printing facility in Australia in order to serve the Oceania and southeast Asian markets.