1.
This is a picture found on a manga website where it looks like that they are advertising their new magazine. Notice that on the right side written in yellow there is "manga" in Katakana （マンガ）. Manga, written as “漫画” in Kanji, is apparently not a foreign word.
Tatsumi Sensei mentioned that many young Japanese people use borrowed words in daily life even though some words exists in traditional Japanese because they think it is fashionable and fun. Therefore, it is very reasonable to think that they use Katakana here to represent the English word "manga" (which probably comes from the Japanese word) in order to give the advertisement a modern and fashionable feeling.
2.
This is a picture of the cover of a book, which seems to talk about the big difference between Japanese people in the western part and those in the eastern part. On the top there is "ビックリ" (meaning "surprise" in English) written in Katakana. This ビックリis by no means a borrowed word. In fact, it is more often written in Hiragana and written as "吃驚" in Kanji, which indicates that it is a native Japanese word.
The reason of using Katakana here seems obvious when we notice the exclamation mark right after the word. Katakana here might play a role similar to the all-capital-letter word "SURPRISE!" Writing this in Katakana can to some extent reinforce the exclamative tone as well as the feeling of "surprise" itself.
Another similar example "コチラ" can be found in the right-bottom of the first picture.
3.
This third example is very different from the first and is just the opposite of the second one. On the top of the label of this facial cleanser, there is “ニキビ”, which means "pimple" or "acne". To no one's surprise, this word is also a native Japanese word, written as "面皰" in Kanji.
Instead of making exclamations, the usage of Katakana here seems to make the word more subtle. Acne and pimple are often considered ugly and not clean. Therefore, instead of writing the word in Kanji, which gives people a straightforward feeling of "facial defect", writing it in Katakana feels like the producers are whispering the word to the customers and trying not to embarrass them. Therefore, using Katakana here makes the label more subtle and polite.
