You may be reading this, thinking MMF2's built-in image editor is perfectly fine.
Well think again - MMF2's image editor sucks.
It's actually missing a heck of a lot of basic tools and other features that will help you make better game graphics, or at the very least help you make graphics of the same quality in a much shorter time and with less effort.

The good news is that there are plenty of really good and totally FREE graphics apps that you can download.



FEATURE SUMMARY

Note that The GIMP and Paint.NET both support plugins which can add some additional functionality - such as animation, effect filters, custom brushes, etc.

Image


MINI REVIEWS

Image-MS Paint-
Screenshot: http://imgboot.com/images/hawker/MSPaint.png

Perhaps the only thing that would actually be a step down from MMF2's picture editor. The only good things about it are that it's probably already installed on your computer, and if you ever do make anything decent with it, it'll be that much more of an achievement.

Overall Rating:


Image-Graphics Gale-
http://www.humanbalance.net/gale/us/
Screenshot: http://imgboot.com/images/hawker/GraphicsGale.png

GraphicsGale has always been quite popular within the klik community, and was designed with animation in mind, with some nice, unique features such as onion-skinning.In addition, it also has all the usual tools and features required for pixelart. It does have a few very basic effect filters, but is certainly not suitable for general graphics work - only pixelart. As an added bonus, it includes an image browser, allowing you to preview images saved in GraphicsGale's own native format (for other images, you may as well just use Windows Explorer).

Unfortunately, the interface is fairly poor. Adjusting tool properties is awkward, and editing a brush even worse. Right-clicking picks a colour, instead of drawing with the secondary colour (which would be more useful), and you can add to a selection but not remove from it. Alpha channels are loaded from a separate image, which is normal but a little tedious for pixelart - I much prefer Paint.NET and Pixelformer's more intuitive system.
Without the animation features, GraphicsGale really wouldn't have much else to recommend it - it would just be another subpar pixelart app - however, if you are looking to animate some small sprites, it might worth a look. Be aware that The GIMP and Paint.NET both support animation through downloadable plugins.

Overall Rating:


Image-Pixelformer-
http://www.qualibyte.com/pixelformer/
Screenshot: http://imgboot.com/images/hawker/Pixelformer.png

As the name suggests, it's very heavily biased towards pixelart, and for that, it really is very good. It has every tool and feature you could ever need, including layers, alpha channels, palettes, easily adjustable brushes, the magic wand tool, multiple-selections, etc - all very well implemented (especially alpha channels). There's even a nifty supersampling feature which makes antialiasing a piece of cake.
The interface is simple and extremely intuitive, although I'm not a fan of the dark grey theme (I know it's supposed to help with choosing colours, but still).
The more I use it, the more I think this is what MMF2's built-in image editor should be like.
Unfortunately, it is seriously limited as a general purpose graphics app, which makes it very hard to recommend when you look at the competition - unless you're a real old skool pixelart purist.

Overall Rating:


Image-The GIMP 2.6-
http://www.gimp.org/
Screenshot: http://imgboot.com/images/hawker/TheGIMP.png

The obvious place to start with The GIMP is the notoriously bad user interface. It is at least highly customizeable, which is great - although that process is not overly intuitive, and may cause a few crashes. It also seems to forget some window positions/sizes when you close the program - meaning you have to slightly readjust everything each time.
Also, right-clicking brings up a menu instead of drawing with the secondary colour, which is a pet hate of mine.
Those annoyances aside, the interface is actually not bad at all, provided you invest the time to set everything up how you like it to begin with.

On to the really good points...
There's no denying The GIMP is a very powerful graphics app. It has a huge range of tools and filters, and a lot of control over all of them (eg. brushes have size/shape/hardness/spikes/aspect ratio/angle/spacing options - although not density for some reason). If you want to do a lot of different graphics work (not just pixelart and general game art), and are prepared to spend a fair amount of time learning, then The GIMP really is the clear winner. On the other hand, many users will not need all the advanced features, and would probably prefer something that doesn't require IKEA-style self assembly.

Overall Rating:


Image-Paint.NET-
http://www.getpaint.net/
Screenshot: http://imgboot.com/images/hawker/Paint_NET.png

Paint.NET doesn't have quite so many advanced features as The GIMP, but it certainly has more than enough, whether you want to do pixelart or photo manipulation or anything else you might throw at it (vector graphics / animation not included). It's just a shame about the lack of adjustable/custom brushes - a surprising omission, considering the wealth of other options that are available (these can be added by downloading a free plugin).
Paint.NET handles alpha channels in a similar way to Pixelformer, with palette entries containing an alpha value in addition to RGB/HSL values (I recommend you set the blend mode to overwrite for pixelart). It's not quite as good as Pixelformer's system though, as there is no way to view just the alpha channel of an image, or the image without the alpha channel - it's still a great system for pixelart, but for general graphics work, you'll again probably want to download a plugin to add that extra functionality.
The interface is very simple and intuitive, with everything where you expect it to be, and nothing requiring more than one or two clicks. Even the toolbars are semi-transparent (in Windows XP), so they aren't wasting any screen space.
Overall, it's a great app, and vastly superior to MS Paint and MMF2's built-in image editor. It's not quite as powerful as the likes of The GIMP, Photoshop and Paintshop Pro, but most people will find it more than adequate, and very user-friendly.

Overall Rating:



CONCLUSION

So, are any of these free apps as good as the commercial alternatives - Photoshop and Paintshop Pro?
In a word, No.
The GIMP comes closest, and while it does pack a lot of features, the features it adds are not that useful, one or two features that would be very useful are absent altogether, and the interface is nowhere near as good. I can do things in Paintshop Pro 9 in a fraction of the time it would take in The GIMP, and that's not just down to my greater familiarity with PSP.

Basically, if you're the kind of person who really needs the power that The GIMP can offer, then you'd be better off trying to get hold of an older version of Photoshop or Paintshop Pro, off Ebay or somewhere.

If you're looking for a powerful and versatile raster graphics app, but you don't need the really advanced features, then go ahead and download Paint.NET - you won't regret it.

Just whatever ever else you do, do NOT use the MMF2 picture editor or MS Paint.