If you use the thumbnails (as opposed to the display or original image) and have the thumbnail style set to square (perhaps with the need to recreate them) then the original image will be cropped where the center part of the image is taken to create the square thumb from. Of course, if you want to show 50x50 thumbs in the RSGallery2 component and want 100x100 squared images in the module this won't work (never make an image larger than it actually is, it reduces the quality and the image will get "blurry").

If you don't want to use the thumbnails you could try a different path: each image is contained in a div with class mod_rsgallery2_latest_galleries-shadow. You could change the CSS styling to include for display images where the smallest size if over 100px:
  height: 100px;
  width: 100px;
  overflow: hidden;
This way the div surrounding the image will be limited in size and the part that the image is bigger than these 100x100 settings won't be shown because of the overflow setting.

To show an example:

• The screenshot part in example_display_images shows four display images, sizes 100x400, 400x100 and two of 266x132. These are images made in paint, that's the reason for their strange sizes  .
  
• Now I can set them all to have the same height of the image in the module settings (I'll take 100px and use the CSS height parameter to adjust the image size): example_display_images_imgHeight100.jpg.
  
• I don't want the images to stretch, but to get squared images I need some kind of cropping, I can use the CSS styling of the div with class
  mod_rsgallery2_latest_galleries-shadow for that:
    overflow: hidden;
    width: 100px;.
  I don't set the height, because that is already done via the backend parameters in the module for the img tag.
  See example_display_images_imgHeight100_divWidht100.jpg (where I've removed the shadow from the CSS file).
  
• Controlling the position to be centered (no example image for this) can be done via CSS styling on the img with class rsg2-displayImage:
   display: block;
   margin-left: auto;
   margin-right: auto;
  and the "float: left" for the div with class mod_rsgallery2_latest_galleries-shadow needs to be removed for this to work. The text can then also be aligned with a "text-align: center;" on the table.mod_rsgallery2_latest_galleries_table (e.g. this is the table with class mod_rsgallery2_latest_galleries_table).
  
• Of course, I can use the display images without the CSS widht/height settings in the backend and just use these CSS settings
    height: 100px;
    width: 100px;
    overflow: hidden;
  in the style sheet (the .css file). Then I get example_display_images_divWidthHeight100.jpg. The drawback is that you cannot control which part of the images is "cropped" this way (is that true? perhaps a position attribute can help?).
  

I'd love to hear if this gets you what you want, but if it's overwhelming and you need more detailed instructions, then post what kind of image you want to use (thumb/display/original) what their sizes overall are and what sizes you want for the images to show in the module.

By the way: I've noticed over time that there never is an "ideal solution (for most users)"  (no offence, just an observation).

Knowing myself I guess in a few night I will wake up in the middle in the night and think "that's how I can implement it nicely in the module..." (happened with your "can I have a second row of images"-question as well .

In the mean time, adjusting the CSS is the only way I can think of, and I'm no CSS styling guru so there may be better ways to achieve what you want. I can only advise to start playing with Firebug on Firefox...

Perhaps nicer: CSS file contents to get images in a div with width 200px, centered, and the "CSS height parameter" is set to 200px in the backend in the module parameters.

I'm using this code plus thumbnail setting in the module and I have exactly what I wanted. Thank you. This is now officially THE best gallery solution for Joomla 2.5! Coupled with CB, I have everything I need for a busy, multi-user, front-end, backend, component and module facilitated gallery. Where do I write the review!?

I'm considering removing the CSS for the shadow around the image (because that doesn't combine for me with setting the height of the div element

I like the shadows but current design trend to not have them. A white border around each thumb would be ideal (however also just taste and not critical — and can be put back with custom coding if required I assume).

and making an extra backend setting where one can set the div height/width.
When that div heigth/widht is then used, it goes in the code itself and not the CSS file (not ideal) and the overflow (that part of the image larger/wider than the div) will be hidden.

Nice.

Also, I want to remove the option to set both height and width of the img element (backend already has a not "not recommended" because it most likely stretches the image).

I don't understand the difference between this and the preceeding suggestion — the difference between div and image.

This combines img sizes and div sizes ... I think this is as flexible as it can be :-) what do you think?

I think it's great. Your coding assistance mod to an earlier version gave me the same effect, as far as I know. This new version does it straight out of the box.