The best way I can think of would be to put them in a table with a width set to 100%. Specify the width of each TD containing an image (so it's set to the width of the image + any borders that may be around it), and then put and empty TD between each image that will automatically resize to fill whatever space there is in between. For best results, make sure every TD is set to padding:0px!important, because heck you, too, tables. To demonstrate:

[table style="width:100%;"][tr]
[td style="padding:0px!important;width:250px;"][img src="IMAGE HERE"][/td]
[td style="padding:0px!important;"][/td]
[td style="padding:0px!important;width:150px;"][img src="IMAGE HERE"][/td]
[td style="padding:0px!important;"][/td]
[td style="padding:0px!important;width:200px;"][img src="IMAGE HERE"][/td]
[td style="padding:0px!important;"][/td]
[td style="padding:0px!important;width:100px;"][img src="IMAGE HERE"][/td]
[/tr][/table]

You probably will want to make a new table for every row, unless the images are all equal width and equal number per row - but I imagine that's not the case if you're not able to make the edges align. :'D