MastifMike said:
" image sizes are 2.8"x3" for Little Chuck and 2.8"x4" for regular Chuck. Even at 72DPI it should look fine (higher DPI would be better and I normally work at 300 DPI b/c while you can shrink it, enlarging can sometimes cause visible issues). All that being said, IMHO, somewhere around 200x300 pixels should be fine for most images."
A slight correction from what I had said, the regular Chuck is 2.8" x 4.5" (NOT 4"). Otherwise, yes the higher the resolution the better as things will get less pixelated and any changes/adjustments are easier when working with higher res. Text especially can be an issue at lower resolutions as the fidelity of the letters becomes less crisp.
So to sum up (my opinion):
72 DPI - Is minimum (and fine for anything that has limited detail and medium to large text)
150 DPI - About as high as necessary as the average human eye isn't really capable of noticing a difference between 150 and higher on a Chuck.
300 DPI - The minimum resolution I'd recommend for actual Photoshop
work, but can still be output at 150 DPI for Chuck purposes or other printing where the higher resolution isn't needed (i.e. billboard are printed at what, something like 10-15 DPI?!?!).
301+ DPI - If source material allows, I do like working at higher resolutions but it's certainly NOT necessary for Chucks. Depending upon what the final output is going to be used for it might just be overkill. However, it's very easy to lower the resolution, but it's not really possible to add resolution, thus why I prefer to err on the high side.