Provide an inline filter for placing attached images into text areas

I don't really see what "thumbnails" (shrunk down tiny versions of images) are going to help here. If you want to see the images inline with your comments, I think the better solution would be to install something like the dme_image module from http://drupal.org/project/dme. It's incredibly simple + lightweight. It just lets you do stuff like this:

<dme:image number=1 align="left" />

This will embed the 1st file attached to the node/comment, wrapped in the appropriate div to float left with reasonable padding, etc. Since these can only reference images attached to the node/comment you're working with, there's no security concern like we have for allowing people to directly use <img> tags, so we can make this filter available in the default input format.

Since it'll automatically generate the markup we want, we can just add site-wide styles to avoid problems like #945992-11: Is a Frontpage post about the redesign launch planned?.

@Bojhan: Sorry, your original request wasn't clear. You just said you wanted "thumbnails".

Even so, I think making people use some minimal markup instead of having it completely automatic is important for a few reasons:

A) Some images are large and overwhelming, and you don't always want them rendered directly inline with your issue or comments. Since we're going to need some way for users to control what appears or not, instead of trying to form alter the file attachment table to add another checkbox and all that, we just let people opt-in to displaying images if they want them.

B) If you have multiple images, it's very good to be able to intersperse your text and commentary on the images, instead of just having a wall of text and a wall of images. For example, here: #936648-30: Make the "My issues" block (for the dashboard) more beautiful and functional

C) Adding a filter like this would solve all kinds of markup problems for case studies and news items. Again, please read #945992-11: Is a Frontpage post about the redesign launch planned?.

D) dme + dme_image already exist, work, and have taken the D7CX pledge to be ported to D7 by the time core 7.0 is out. What you're talking about would probably require more d.o-custom code that'd have to be maintained + ported.

Also, we can simplify the markup, e.g. it'd be align left by default... So, all you'd need would be <dme:image number=2 /> Or even just <dme:img number=2 /> or something. I'm not 100% attached to DME, I just happen to know it and use it myself, so I have direct experience with it...

Granted, from the UX perspective, you only care about A-B. But even if that's all you care about, A-B are still important. However, UX isn't the only concern on d.o, so the other considerations are also important...

The documentation team wants to have a way for normal users to add images to Handbook pages, and that issue has been closed as a duplicate of this one:
#995354: Docs format and Docs role - figure out what to do

Adding tags so we can track on this issue instead.

Is the proposal here to allow any user to add images via some inline filter in the "Filtered HTML" input format, or would this inline filter only be available to users who request the "documentation" or "with image" input format (or whatever it's called)?

The proposal on #995354: Docs format and Docs role - figure out what to do was that we wanted any user who had been on drupal.org for a month or more to automatically be given permission for some method to upload and insert images. We'd like to avoid having to make people go through a request to get this permission, and we'd probably also like to avoid becoming an image spam magnet by letting anyone create an account and immediately start uploading images.

Sorry, just noticed this is duplicate with an older, basically identical proposal: #528682: Allow inline images to be posted to Drupal.org project pages, docs pages, and comments without any special permissions