They are a combination of regional variation, and foreign accent, depending on the context.
When in the context of native speakers, what you are referring to is the Ich-Laut
Many Germans in regions which historically spoke Low German languages, such as Berlin, pronounce ich [ɪk]
Germans from regions which historically spoke Ripuarian-Germanic languages, or Germans who still speak a Ripuarian-Germanic language (such as Kölsch) as their first language, pronounce ich [ɪɕ], [iɕ] or [iʃ] [ɪʃ]. The vowel can change a bit.
Native High German speakers, from regions that have spoken High German for hundreds of years, and speakers who want to emulate them pronounce it [ɪç]. [ç] is sort of like the palatalized English h-sound in the word "hue", but at the end of a word.
From experience, many German speakers in Berlin will say it [ɪk] but mich [mɪç] because saying "Mick" is very stigmatized and sounds, as one German speaker put it, like "Mickey Mouse".
Native English speakers tend to pronounce those words like [ɪk] or [ɪʃ].
