I just knew that Flickr doesn’t like people to upload screenshots or design images. But it allows you to do it. What you need to do is to set the proper content type before uploading.
Above the “UPLOAD” button, there is the link “Show advanced settings…”. Click it and you can select the correct type of the images.

Unfortunately I haven’t found it before. I have uploaded many screenshots (about 40). I have to change the images’ content type one by one. I found how to do it. Its help says:
You can also change the Content Type after you’ve uploaded your screenshot, either using the “Flag your photo” link under Additional Information on a photo page, or in the Organizr.”
So, don’t forget to select the corrent content type before uploading pictures, especially for screenshots.
Tags: Web