I have created several images for Wikipedia and would like to use them for my own poster/talks as well. However I am concerned that my colleagues will assume that I took them from Wikipedia and will consider it bad practice to use images from Wikipedia instead of my own and secondly to not reference them. How would you clarify that?
I think the problem here is that you (a) don't feel like you should be citing the source of this, since you made it yourself but (b) think this will be viewed as plagiarism from Wiki (or, at least, laziness). It seems to me the best way to resolve this is to cite your source, and cite it as yourself via Wikipedia. A short note like (Wikipedia, Original Artist Jane Doe) makes it clear that yes, this is the image from the Wiki page but also that you made it.
When using images from Wikimedia Commons (where they are usually actually hosted) you have to consider two aspects: (i) the license, (ii) scientific citation rules.
(i) is not an issue if you are the creator of the image and it is an original work (and not a derivative of another work). You have not granted rights to Wikipedia for exclusive use of your work (as you would to a journal). Therefore, you don't need permission to use your own images. In practice, you'd need to be able to prove that you are the creator, but if you still have the log-in of the user account that's not a problem. It's even easier if you have released the images into the public domain. If your image is derivative work, the license of the original work(s) applies.
Since you have published the images on Wikimedia Commons and apparently have added them to a Wikipedia article, I would interpret (ii) as requiring self-citation in the same way as if you had used the images in a previous scientific publication of yours.
Obviously, this means that you can't keep the anonymity of your Wikimedia user account, but that doesn't seem to be a concern for you. If it was a concern, you would need to cite it as someone else's work and also follow the requirements of the license.
Thus, I would cite the source like this (adjust to your style):
Image contributed to Wikimedia Commons by me using the pseudonym "Jannick". First used in Wikipedia article "Very important topic" (2015).
Finally let me say that I consider contribution to a free encyclopedia such as Wikipedia a laudable effort. If I saw something like this in a talk or on a poster, I would regard it favorably. However, there are possibly people that consider contribution to Wikipedia wasted effort that would be spent better on writing scientific publications. Decide for yourself if you care about their opinion (I don't).
Good question, but one part is not entirely clear: do you prefer to remain anonymous/pseudonymous on Wikipedia?
If you don't care, the best solution is to log into your account, and update the Wikipedia or Wikimedia Commons page to reflect your full name. Here is an example of the best code to do that, at least on Commons.
If you do prefer to remain anonymous, your problem substantially results from your having contradictory wishes: on the one hand, you don't want the general public to link your Wikipedia avatar with your real-world identity, while on the other hand, you do want a loosely-defined subset of the general public to make that link. So, the more broadly you communicate the full story, the more you risk "outing" yourself to the general public. There's no "right answer," as any answer will require a judgment call on your part, of how much risk you're willing to endure.