The number of screenshots you should submit depends on whether a (regular) test report or a Bug is concerned. For guidelines about Bug Approvals, see the separate entry. You will usually not be able to submit anything if you have not added enough screenshots.
Test report: For the test report, so-called "alibi-screenshots" are required. We need to see that you covered all relevant parts of the test. In these screenshots you can for example show the positive/negative aspects you mentioned in your report. In the test description, we will often tell you the minimum amount of screenshots required for that test.
Bug: Screenshots are vitally important in order for us to understand which steps led to the Bug and reproduce it. When in doubt, it's better to make more screenshots than too few. In case of malfunctions, a screencast can usually show the problem better.
Important:
Always try to create a connection in the text to the screenshot you are referring to!
Only upload screenshots in the formats png, gif, jpg or jpeg!
Please make sure that the screenshot shows the complete window. This also includes the URL of the test website.