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This Q&A is part of a weekly series of posts highlighting common questions encountered by technophiles and answered by users at Stack Exchange, a free, community-powered network of 100+ Q&A sites.

It's a response often encountered during technical interviews: "OK, you solved the problem with a while loop, now do it with recursion." Or vice versa. Stack Exchange user Shivan Dragon has encountered the problem and he knows how to answer: show that you're able to code both ways. Give the interviewer what he wants. But which method is generally preferable? A few more experienced programmers respond.

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Design A Website 1 Designing A Website Above The Fold
What is the fold and how does it affect your website? There has been much discussion over the years about what should be kept ‘above the fold’ and how much importance it really has. With the rise of mobile internet browsing, the boundaries of the fold are forever changing. While there may not be a definitive answer, we have put together this infographic to help you get a clearer picture of how the fold is affected and points to bear in mind when designing your website.

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I'm proficient at programming, though there are still things I'm not entirely comfortable with (function pointers, what?), but the largest gap in my knowledge is of algorithms. I competed in ACM my freshman year of college and did pretty well (second place at a small competition, 5th at a slightly larger one), but that was largely because I had a teammate who had a huge binder of algorithms for the complicated problems. I've gotten a little burned out on figuring out my own solutions to problems I know have been solved, and I want to learn some of those solutions. What should I learn?

(I know sorting algorithms, and I've heard a little about fancier things like edit distance and such. I'm interested in data processing currently; smoothing, approximating, best-fitting, etc. Currently trying to work on something to predict/learn trends--how it's changing, how fast it's changing, and how long that change will last. I'm interested in algorithms in general though.)

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Dutch artist Sebastien Schmieg has elevated the Google Image search from its humble intent, creating a short film that strings together a series of image searches. The result oscillates between the prosaic and profound, and feels more like a grand homage to humanity than a collection of random images.

To create the image sequence Schmieg fed a single transparent PNG into Google Images and used the “visually similar” feature to recursively loop through the results. Schmieg’s movie of the results, entitled Search by Image, Recursively, Transparent PNG, #1, is a (slightly NSFW) truly hypnotic, algorithmic tour of life as Google Images knows it.

In all there are some 2,951 images in the video. The “visually similar” option in Google Image Search tends to get stuck in loops using it the way Schmieg did so if an image had already been used in the sequence, he would skip to the next image in the results. But otherwise the sequence is entirely algorithmic. Beware pareidolia.

For more info about the movie and some other, similar efforts, be sure to check out Schmieg’s website.

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Droste Effect refers to an artistic technique that creates a recursive picture in which a smaller version of the image is placed inside itself repeatedly. In still images, the recursion is limited by the fixed resolution of the picture but can repeat as an infinite loop in animations.


Art History

According to Wikipedia[1], the first known Droste effect image was a triptych from 1320 by Italian artist Giotto di Bondone called the “Stefaneschi Altarpiece.” In the painting, the Cardinal Giacomo Gaetani Stefaneschi is holding the exact same painting he is featured in. The name for the technique originates in 1904 from the cover art for the Dutch Droste cocoa powder that featured a nurse holding a serving tray with the same box of cocoa powder on the tray.

Animated GIFs

Droste effect animated GIFs can be made to loop so that it appears to be infinitely zooming in on the image. One of the earliest known Droste effect GIF fads was inspired by an image called “Fractal Grandma” that featured a woman in a blue shirt wearing a duplicate of herself on her hand. The first known posting of the image comes from a post on the image site Moonbuggy[2], that was cached by Google on November 7th, 2007. A YTMND page using the same image titled “Recursive Grandmother”[3] was created on May 6th, 2008. On September 3rd, 2009, an edited version with Gary Busey’s head was posted to YTMND.[4]


Several pages worth of Droste effect images can be found on Tumblr[10], Flickr[8] and deviantArt.[7] The first relevant deviantArt[13] image was titled “Picture in Picture” and was posted by user nlife on November 26th, 2004. The first Droste effect Flickr[14] image was titled “Honey I Escherized the kids!” and was submitted by user Seb Przd on July 6th, 2006. An explanation of the mathematics behind the Droste effect was posted to the Mathematical Imagery[6] blog on December 26th, 2008. A round-up of Droste effect images was posted to the photo blog Pixzii[5] on December 31st, 2009. A Facebook[9] fan page has 113 likes as of November 15th, 2011.

Usage in Video Art

The collaborative art project Zoomquilt[11] that featured a looped zoom flash animation taking the viewer through several different paintings was created in 2004. The sequel Zoomquilt 2[12] was published in November of 2007.

The music video directors Alex and Martin made a Droste effect style video for the song “Seven Nation Army” by the rock band The White Stripes in 2003. The video appears as if it is one long shot that zooms into a tunnel of black, white and red triangles.

On September 2nd, 2008, a music video was uploaded to Vimeo using the Droste effect by user OneInThree for the song “Brave Bulging Buoyant Clairvoyants” by the Wild Beasts. On September 8th, 2008, Director Frank Beltrán uploaded a Droste effect music video to Vimeo for the song “Clap your brains off” by the Mexican band No Somos Machos Pero Muchos.

Search Interest

External References

[1] Wikipedia – Droste Effect

[2] Moonbuggy – Fractal Grandmother

[3]YTMND – recursive grandmother


[5] Pixzii – 20 Illusional Droste Effect Images that will Twist Your Mind

[6] Mathematical Imagery – The mathematics behind the Droste effect

[7] deviantArt – droste

[8] Flickr – drost effect

[9] Facebook – Droste effect

[10] Tumblr – #droste

[11] – Zoomquilt

[12] Mad Mind Worx – Zoomquilt 2

[13] deviantArt – Picture in picture

[14] Flickr – Honey I Escherized the kids!

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